# Eric P. Verrecchia · Luca Trombino

# A Visual Atlas for Soil Micromorphologists

A Visual Atlas for Soil Micromorphologists

Eric P. Verrecchia • Luca Trombino

# A Visual Atlas for Soil Micromorphologists

Eric P. Verrecchia Institute of Earth Surface Processes University of Lausanne Lausanne, Switzerland

Luca Trombino Department of Earth Sciences University of Milan Milan, Italy

ISBN 978-3-030-67805-0 ISBN 978-3-030-67806-7 (eBook) https://doi.org/10.1007/978-3-030-67806-7

© The Editor(s) (if applicable) and The Author(s) 2021. This book is an open access publication.

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*For Milena*

### **Foreword**

Micromorphology, the microscopic investigation of undisturbed earth materials, is by definition based on the ability to identify components and to recognize shapes, arrangements, and patterns in thin sections. Microscopic observation is complicated by the fact that a two-dimensional image is used to observe a three-dimensional reality. A book with reference images can, therefore, be of invaluable importance for micromorphologists.

In the past, handbooks on micromorphology were sparsely illustrated with black and white photographs. It is only since the beginning of this century that the use of colour plates became economically feasible. Although some initiatives were taken to make more reference images available for students and researchers, they only reached a limited audience.

In life sciences, such as medicine, biology, botany, and wood anatomy, atlases of microscopic images have existed since the early twentieth century, the earliest of which often included coloured drawings. Similarly for mineralogy and petrography, atlases of rocks and mineral images under the microscope were published in the second half of last century and were used with enthusiasm by generations of students. Such an atlas is missing for soil micromorphology. The initiative taken by Eric Verrecchia and Luca Trombino is, therefore, more than welcome. This atlas has been prepared not only for beginner soil micromorphologists but also for more experienced researchers. Images are complemented by informative text explaining concepts and terms, and by references to the literature, and where necessary, a historic insight into the evolution of the terminology. A list of translations of the terms into French, Italian, and German at the end of the book will contribute to widen its use internationally.

Ghent, Belgium Prof. Em. Georges Stoops

#### **Acknowledgements**

Many people provided samples or thin sections to complement our own collection, which were indispensable to be able to illustrate the large variety of features observed in thin sections of soil: Yann Biedermann (UniNe1), Dr. Filippo Brandolini (UniMi2), Dr. Guillaume Cailleau (DataPartner, CH), Prof. Mauro Cremaschi (UniMi), Dr. Nathalie Diaz (Unil3), Dr. Fabienne Dietrich (Unil), Prof. Alain Durand (Université de Rouen, F), Dr. Laurent Emmanuel (Sorbonne Université, F), Dr. Stephania Ern (Cantone Ticino, CH), Dr. Katia Ferro (UniNe), Prof. Karl Föllmi (Unil), Prof. Pierre Freytet<sup>4</sup> (Université Paris-Sud Orsay, F), Prof. Jean-Michel Gobat (UniNe), Dr. Stephanie Grand (Unil), Céline Heimo (UniNe), Dr. Guido Mariani (UniMi), Dr. Loraine Martignier (Unil), Dr. Anna Masseroli (UniMi), Dr. Ivano Rellini (Università degli Studi di Genova, I), Rémy Romanens (Unil), Dr. David Sebag (Université de Rouen, F and Unil), Dr. Brigitte Van Vliet-Lanoë (CNRS, Université de Bretagne Occidentale, F), Prof. Andrea Zerboni (UniMi), and Dr. Luisa Zuccoli Bini (MIUR, I).

Soil micromorphology will continue to need the talent of gifted technicians, engineers, and researchers. We would like to thank our colleagues who provided documents or spent time with us on specific techniques: Dr. Benita Putlitz (Unil), Dr. Daniel Grolimund (PSI, CH), Dr. Kalin Kouzmanov (Université de Genève, CH), Dr. Laurent Remusat (Muséum National d'Histoire Naturelle, F), Dr. Alexey Ulyanov (Unil), and Dr. Pierre Vanlonthen (Unil). We would like to thank the students of the MSc in Biogeosciences program (Universities of Lausanne and Neuchâtel) who kindly chose the title of this Atlas and tested its draft version, Titi, Scintillina, and the Dragon for their valued support.

The authors benefited from funding through different sources during the making of this Atlas, which has been written in Lausanne within the framework of a scientific agreement between the universities of Lausanne and Milan (special thanks to Denis Dafflon and Marc Pilloud, International Relations, and Prof. François Bussy, the Faculty of Geosciences and the Environment, all from the University of Lausanne). The *Fondation Herbette* funded stays for Prof. Luca Trombino in Lausanne. The Swiss National Science Foundation made possible free access for the e-version of the Atlas by funding a Gold Open Access agreement with Springer-Nature. Special thanks to Zachary Romano (Springer-Nature), who believed in our project, supported us, and edited our Atlas. His help and his kindness made this adventure much easier. Finally, we would like to thank Karin Verrecchia for her endless patience and her careful proofreading of the manuscript.

If Prof. Georges Stoops had not been such a great scientist, a wonderful teacher, and such an endearing person, the authors would have never met and probably not considered soil micromorphology to be as important and relevant as it really is. Thank you Georges for your endless help and consideration.

<sup>1</sup> UniNe stands for Université de Neuchâtel, Switzerland.

<sup>2</sup> UniMi stands for Università degli Studi di Milano, Italy.

<sup>3</sup> Unil stands for Université de Lausanne, Switzerland.

<sup>4</sup> Profs Karl Föllmi and Pierre Freytet sadly passed away shortly before the publication of this Atlas.

#### **Introduction to the Atlas**

#### **Why Use Such an Atlas?**

Natural sciences are based on the observation of natural objects. The precise description of their characteristics is fundamental in order to establish nomenclatures. From these nomenclatures, the study of the processes at the origin of their distinctive features allows classifications: classifications are built using qualitative, quantitative, and semi-quantitative parameters of specific features, which allow hierarchical relationships between objects to be drawn. Consequently, before pretending to understand the origin of a natural object, it is necessary to identify its borders, describe its properties, and compare it to other similar objects belonging to the same nomenclature. Soils are no exception. Unfortunately, many soil scientists contend that going directly from the hand lens observation in the field to the mass spectrometer analyses in the lab fills all the requirements for a suitable and thorough investigation. They are wrong.

Indeed, soils constitute a unique and emergent property of the complex interactions between life and mineral matter. Only looking at soils from the inside, in their minute detail and at various microscopic scales, allows soils to be explored with the best acuity. A simple example: measuring the amount of calcium carbonate in a soil does not say anything about the location and origin of this calcium carbonate. Is it along the pores, as tiny nodules or in the groundmass as impregnations? Is it micrite or needle-fibre calcite associated with fungi, a sparitic coating or calcified root cells? All this information is not available if the investigator cannot observe the structure of the objects themselves, using the appropriate tool. Crushing and grinding a soil sample to a very fine powder provides information about its chemistry and the nature of some of its compounds but reveals nothing about the relationships, the organization, and the hierarchy of the various features and objects that constitute its architecture and record its history.

Moreover, according to Richter and Yaalon (2012), soils are all polygenic paleosol systems, superimposed over time, forming a sort of palimpsest. Therefore, there are traces of old mechanisms, like a permanent background noise, which alters the geochemical signal of the contemporary dynamics. Consequently, the question must be asked: how much importance should be given to "blind" (i.e. bulk) geochemical studies that consider the soil as a functional, single-phase continuum? What is the meaning of using, for example, the τ factor (Brantley et al., 2007), when the parent material remains as a trace component or a phase impossible to clearly identify and when the bulk fraction results from a diachronic mixture? A better method would be to consider the use of soil micromorphology, which allows the soil to be seen from the inside and to identify the traces of past pedogenesis. Such an approach would allow the geochemical analyses to target objects indicative of such past pedogeneses. This method requires an extensive experience to address the qualitative issues related to the selection of the pertinent and most promising pedofeatures. It justifies further access to often expensive equipment (micro-drill sampling, microprobe and synchrotron investigations, mass spectrometry on very small quantities, laser-ablation ICP-MS on thin sections, etc.), in order to quantitatively characterize the elementary dynamics at work in the selected pedofeatures and recombinations of trace quantities. In conclusion, soil micromorphology affords most of the necessary tools, vocabulary, and methods of observation that will facilitate the investigations. This practical Atlas aims at providing the necessary comparative and visual references to guide the soil micromorphologist in her or his identification of the various soil objects observed under the microscope. It does not aim at providing interpretations. Instead, it proposes to relate concepts and vocabulary of soil micromorphology to images of the real soil world. Therefore, the Atlas helps the micromorphologist to apply concepts and vocabulary in a rigorous manner by using comparisons between her or his own thin sections with a collection of examples. Nonetheless, Stoops et al. (2018) presented a comprehensive reference for interpretations, once features have been properly described and identified. This Atlas is, therefore, complementary and must be used before opening Stoops et al. (2018).

This Atlas is designed for researchers, academics, and students at the master's and doctoral levels, so they can rapidly find features and structures observed in thin sections of soil. It is convenient for fast self-instruction by using comparative photographs. Therefore, it can also be used in the classroom as a visual resource book, the eye being the best tool for learning natural features by intuitive links of shapes and colours, or as a reference for comparisons in advanced studies. Therefore, this Atlas provides a basic background to build a pertinent nomenclature, which will help to identify the process-oriented challenges associated with soils. Finally, the reader must keep in mind that soil micromorphology is more than a scientific method to investigate soils. It is also a way of envisaging natural sciences. The method itself requires time, in contrast to a lot of today's "fast science". The soil micromorphologist has to wait for the thin section fabrication and then has to spend hours with the microscope, acquiring the experience necessary to identify the myriad features that appear in nature. This is the profession of the *The Slow Professor*. 5

#### **Online Database and Digital Resources in Soil Micromorphology**

Although many websites are available for images of rock-forming minerals under the microscope, there are only a few dealing with soil micromorphology, e.g. edafologia.ugr.es/english/index.htm or spartan.ac.brocku. ca/~jmenzies. Moreover, there are many websites describing and explaining the principles of optical microscopy: the following webpage of the Soil Science Society of America proposes a large choice of such websites: www. soils.org/membership/divisions/soil-mineralogy/micromorphology. Georges Stoops' handbook, in its first edition (Stoops 2003), was accompanied by a CD-ROM with many micromorphological images. Unfortunately, today, most computers do not include CD-ROM readers anymore, so it seemed necessary to provide soil micromorphologists with an atlas in the form of a printed book and/or an e-book with high-resolution images. Indeed, this Atlas is available as an *Open Access* pdf section at the Springer-Nature website: the high-resolution images provide details at high magnification making the e-book easy to use during observations on a tablet computer.

Today, access to powerful computers makes possible the use of image analysis to quantify features and textures. Most of these software are presently proposed as multiplatform applications. Over the last few years, ImageJ (http://imagej.nih.gov/ij/download.html), or its bundled version Fiji (https://imagej.net/Fiji), became one of the most used freeware in image analysis. It replaces NIH-Image, its ancestor, but some of the macros can still be run on the appropriate version of computers (Heilbronner and Barrett 2014). Gwyddion (http://gwyddion.net/) is another freeware that can be used in image analysis. For people who like to generate code, Scilab remains an extremely interesting open-source solution (http://www.scilab.org/) and can advantageously replace the powerful and user-friendly, but costly, Matlab-<sup>R</sup> . Of course, there are multiple commercial software, some of them being sometimes fairly expensive and provided as a closed system. Therefore, this choice is not necessarily the most appropriate for teaching and research in the academic environment.

<sup>5</sup> Berg M. and Seeber B.K. (2016) *The Slow Professor—Challenging the Culture of Speed in the Academy*. University of Toronto Press. Toronto, Canada.

#### **How to Use This Visual Atlas**

#### *Terminology Used in the Atlas*

The micromorphological terminology used in this Atlas is mostly based on Stoops (2003, 2021). Nevertheless, some concepts or keywords also refer to Bullock et al. (1985) and Brewer (1964), as they provide complementary vocabulary and a different kind of logic applied to the description. Older textbooks contain the descriptions on which most of the present-day soil micromorphology was built. They are just as pertinent today and should not be overlooked.

#### *Book Structure*

The Atlas is organized into six chapters (including Annexes), and each chapter is divided into sections. Each section contains a series of images, usually eight, on the left-hand page, and an explanatory text on the righthand page. Regarding the microphotographs, they are usually displayed in plane-polarized light (PPL) and crosspolarized light (XPL), if not specified otherwise. PPL and XPL views are usually presented as two halves of the same microphotograph, separated along the diagonal. The upper half is always the PPL view and the right lower, the XPL one. Moreover, microphotographs are shown as observed under the microscope, without any alteration, such as arrows, letters, or numbers. The choice of pristine images, such as in MacKenzie et al. (2017), has been made in order to provide self-explanatory views. The text on the right-hand page supplies all the needed information and/or explanation. In addition, each chapter is introduced by a short paragraph in a grey box summarizing the main concepts. All the microphotographs, if not mentioned otherwise, have been taken with an Olympus BX53 polarizing microscope or an Olympus stereomicroscope SZX16 system, both equipped with an Olympus DP73 digital camera operated by Olympus cellSens imaging software.

The six different chapters of the book are devoted to different aspects of the micromorphological approach to studying soils. The technical aspects are presented in Chap. 1: they consist of the sampling strategy for soil profiles, the preparation of thin sections, the various tools used in optical microscopy, and finally the micromorphological approach, which is detailed in a flow chart. The second chapter is related to the organization of soil material, i.e. the fabric, the c/f related distribution, aggregates, voids, and microstructures. In Chap. 3, both mineral and organic constituents are presented in terms of size, sorting, and shape. In addition, this chapter introduces their various natures, whether they are rocks, mineral micromass and grains, biominerals, anthropogenic features, or organic matter. The fourth chapter is a list of pedogenic features as imprints of pedogenesis, presented according to their nature and morphology, e.g. clay coatings, biogenic infillings, or iron nodules. The fifth chapter provides some examples of features associated to the main soil processes observed in thin sections: the imprint of water, the influence of clays, the precipitation of carbonate, gypsum, and oxyhydroxides, and biogeochemical processes. The short Chap. 6 presents a view of what the future of soil micromorphology could be when thin sections are used with instruments other than the conventional optical microscope, such as electron microprobes or laser-ablation ICP-MS. Finally, the Annexes list the formula of the main soil minerals, present some common errors and pitfalls, and propose a way to describe thin sections accurately. A four-language list of micromorphological terms, which can be used to facilitate translations, is found at the end.

#### **References**

Brewer, R. (1964). *Fabric and mineral analysis of soils*. London: John Wiley and Sons.

Bullock, P., Fedoroff, N., Jongerius, A., Stoops, G., & Tursina, T. (1985). *Handbook for soil thin section description*. Wolverhampton: Waine Research Publications.

Brantley, S., Goldhaber, M., & Ragnarsdottir, K. (2007). Crossing disciplines and scales to understand the critical zone. *Elements, 3*, 307–314.

Heilbronner, R., & Barrett, S. (2014). *Image analysis in earth sciences*. Berlin: Springer-Verlag.


#### **Contents**





## **About the Authors**

**Eric P. Verrecchia** is a full professor of Biogeosciences at the Faculty of Geosciences and the Environment, University of Lausanne (Switzerland). He is specialized in geopedology and biogeochemistry of the terrestrial carbon and calcium cycles. Awarded by a Marie-Curie Fellowship for Senior Researchers in 1994–1995, he joined Prof. G. Stoops' laboratory of soil micromorphology at the Ghent University (Belgium), where he was introduced to this microscopic approach to study soils. Since then, he applied this technique, coupling it with biogeochemical methods, to soils from the tropics to the temperate zone, particularly in calcium- and carbonate-rich environments.

**Luca Trombino** is professor in the Earth Sciences Department at the Universita degli Studi di Milano (Italy). His main research topics are in the field of paleopedology, soils, and archaeological deposits, where he extensively uses thin section micromorphology, coupled to sedimentology and Quaternary geology methods. He started to practice soil micromorphology in 1994 when he attended the courses by Prof. G. Stoops at the Ghent University (Belgium) and, at present, is teaching Micropedology to the students of M.Sc. in BioGeoSciences and M.Sc. in Conservation Science at the University of Milan.

## Chapter 1

#### **Observation of Soils: From the Field to the Microscope**

#### **File 1: The Multiscalar Nature of Soils**

As emphasized by W. Kubiëna, ". . . there exists no other method capable of revealing the nature and complexity of soil polygenesis in so much detail as thin-section micromorphology and at the same time enabling one to follow and explain its formation...". This sentence, cited by Fedoroff (1971), highlights the aim of soil micromorphology: looking at a soil from the inside and at various scales, from the optical microscope to synchrotron imaging. Soils constitute multiscalar objects by definition, from their soilscape (at the landscape scale), to their profile and its horizons to the atomic interactions between the smallest minerals and organic molecules. Micromorphology enters the soil investigations at the multi-centimetre scale (see "File 3") at which the thin section is made. The scales of observation span from the millimetre to the micrometre, and even down to the nanometre using electron microscopy (see "File 7" and "File 8"). Therefore, the micromorphological approach is based on multiscalar observations because the different features and properties of soils require different magnifications; in addition, this approach is twofold using composition and fabric (see "File 9").

Cartoon from the Larsen's Far Side. This cartoon has been published in the Proceedings of the International Working Meeting on Soil Micromorphology in San Antonio, Texas, July 1988.

#### File 2 History of Micromorphology

#### **File 2: History of Micromorphology**

Soil micromorphology is a relatively recent method, first popularized by a book by Kubiëna (1938). This method revolutionized the way that a soil was observed because it was studied from the inside, i.e. the inner organization. Indeed, during the "Symposium on the Age of Parent Material and Soils", in 1970, Walter Kubiena, the father of the micropedology, stated: "... there exists no other method capable of revealing the nature and complexity of soil polygenesis in so much detail as thin-section micromorphology and at the same time enabling one to follow and explain its formation ..." (Fedoroff 1971).


#### **File 3: Observation and Sampling of Soils**

There are various ways to sample soil profiles in the field to get the right soil portion of interest that represents the horizon variability. Sampling can focus on horizons, transitions, or specific soil features. The most conventional sample selection is based on the use of Kubiëna boxes of various shapes, sizes, and compositions. They are mainly used in soils with fine textures. However, the soil texture can sometimes be an obstacle to conventional field sampling: a manual block extraction sampling technique is then performed in order to get enough soil material for further impregnation in the laboratory. Moreover, a plaster-impregnated patch of burlap can be used to encase and sample a large block of undisturbed soil (Goldberg and Macphail 2003).


#### **File 4: How to Make Thin Sections**

The micromorphological observation of soils starts with the fabrication of thin sections. This process is generally long because soil samples must be impregnated to solidify them: a polystyrene-based resin, often with a density close to water, is poured on samples. With time, it will penetrate inside the soil pores and harden. Making thin sections requires some specific equipment. The series of photographs included here provides only the major steps involved in thin section preparation. For more information see Murphy (1986) and Benyarku and Stoops (2005).


#### **File 5: The Polarized Light Microscope**

In order to perform micromorphological observations, the polarized light microscope is the most appropriate tool. It couples the magnification of a conventional optical microscope with light polarization induced by a polarizer and an analyser located along the optical light pathway. Micromorphologists use the optical anisotropic properties of soil constituents for their identification and the observation of their potential transformation.


#### **File 6: Other Techniques of Observation**

In soil micromorphology, not only are observations made in transmitted light but incident light is also used. The two most common techniques refer to fluorescence and cathodoluminescence. The source of light in fluorescence is usually an intense high-pressure mercury lamp ranging from 50 to 250 W. A high energy electron beam is the source of excitation in cathodoluminescence at a voltage between 10 to 20 kV. This equipment needs adaptation for the polarized light optical microscope.


#### **File 7: Electron and Energy Imaging**

Soil micromorphologists can use the scanning electron microscope (SEM) to create images of features observed in thin sections. Not only can they access images at high resolutions, in order to see the minute structure of minerals and organic matter, but it is also possible to get information regarding the chemical composition of features. Electron probe micro-analyses (EMPA) are commonly performed to generate maps of chemical element distributions, whereas, transmission electron microscopes (TEM) are usually used to observe e.g. the structure of clay minerals or oxyhydroxides (see "File 78").


#### **File 8: Colours of Minerals**

When using a polarized microscope, light, which vibrates in a single plane, passes through the anisotropic minerals of the thin section (see "File 5"). Then, it splits into two beams perpendicular to each other, as it crosses the minerals, and propagates at different speeds according to the two refractive indices. The two vibrations emerge out of phase and pass through the analyser, which leads to the disappearance of certain wavelengths and to a resultant one, which defines the polarisation colour.


#### **File 9: The Micromorphological Approach**

The micromorphological approach is based on multiscalar observations of both composition and fabric. The chart is derived from the approach proposed by Stoops (2003). The oval boxes refer to input and output of the flow, the diamonds to decisions, rectangles to an identification process, and rounded rectangles to objects.

*Captions from top to bottom.*


**Open Access** This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http:// creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution, and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

## Chapter 2

#### **The Organization of Soil Fragments**

#### **File 10: Concept of Fabric**

Kubiëna (1938) was the first to introduce the concept of fabric in soil micromorphology, so this term has been used in soil micromorphology for a long time. The term "fabric" was initially applied to rocks by geologists and petrologists. This type of fabric is defined as the "factor of the texture of a crystalline rock which depends on the relative sizes, the shapes, and the arrangement of the component crystals" (Matthews and Boyer 1976). This definition has been adapted for soil micromorphology and its latest definition has been given by Bullock et al. (1985) as: "soil fabric deals with the total organization of a soil, expressed by the spatial arrangement of the soil constituents (solid, liquid, and gaseous), their shape, size, and frequency, considered from a configurational, functional and genetic view-point". In conclusion, the soil micromorphologist should consider the fabric as an arrangement and*/*or organization of soil constituents.

Fabrics can be very complex and this concept can be encountered in many different circumstances. For instance, the concept of fabric is mainly related to soil microstructure (see "File 9", "File 20", and "File 21"), but also associated to the c/f related distribution (see "File 13" and "File 14"), b-fabric (see "File 45" and "File 46"), as well as pedofeatures (see "File 9" and Chap. 4). Generally speaking, the fabric is related to the type of light used, as well as the scale of observation, i.e. the magnification of the microscope lens (see "File 11").

Examples of various fabrics related to the main c*/*f distributions (see "File 13"). All microphotographs are in PPL.

#### **File 11: Multiscalar Approach to Fabric**

Fabric is a multiscalar concept that is used to describe homogeneous and heterogeneous units. The example given in this section shows fabrics observed at various magnifications with different soil components and features. Fabric units are units delimited by natural boundaries, visually homogeneous at the scale of observation and distinct from other fabric units (Bullock et al. 1985; Stoops 2003). However, increasing the magnification leads to an increase in either homogeneity or heterogeneity, depending on the fabric and feature involved.

*1., central view; 2.–3., upper views; 4.–5., lower views.*


#### **File 12: Basic Distribution Patterns**

A pattern is the spatial arrangement of fabric units (Stoops 2003). Two types of patterns are usually defined: the distribution patterns and the orientation patterns. This section illustrates the basic distribution patterns commonly observed in thin sections, which are the distribution of fabric units of the same type with regard to each other (Stoops 2003).


#### **File 13: c/f Related Distributions I**

The c/f related distribution refers to the distribution of coarse fabric units compared to fine fabric units and, if applicable, their associated pores. It has to be emphasized that this concept is purely descriptive and does not consider the interpretation of such fabric units. Stoops and Jongerius (1975) proposed a bipyramid of tetrahedra to summarize the basic c/f related distribution. This geometrical shape is modified and used in this section to illustrate the main c/f patterns.

*Captions given clockwise from the upper top picture. All microphotographs in PPL.*


#### **File 14: c/f Related Distributions II**

The c/f related distribution refers to the distribution of coarse fabric units compared to fine fabric units and, if applicable, their associated pores. It has to be emphasized that this concept is purely descriptive and does not consider the interpretation of these fabric units. This section shows different variations in chitonic, gefuric, and porphyric c/f related distributions.


#### **File 15: Aggregates and Aggregation**

Aggregation and aggregates (also called peds) are directly related to the soil structure. Their role is fundamental in defining soil properties, as aggregates are typically a product of pedogenesis. Aggregates are bodies separate from the soil groundmass, clearly delimited from each other and/or the surrounding soil material. In soil microscopy, they are first defined by their morphology.

*Captions from top circle clockwise to lower right corner.*


#### **File 16: Degree of Separation and Accommodation of Aggregates**

Aggregation and aggregates (also called peds) are directly related to the soil structure. Their role is fundamental in defining soil properties, as aggregates are typically a product of pedogenesis. Aggregates are bodies separate from the soil groundmass, clearly delimited from each other and/or the surrounding soil material. In addition to their morphology, they are also defined by their degree of separation and accommodation. The degree of separation refers to preferential zones of weakness illustrated by voids in soil microscopy. The accommodation is the degree to which adjacent ped faces coincide in a complementary way.

*Captions from upper left corner to lower right corner. All microphotographs in PPL.*


#### **File 17: The Nature of Voids**

Voids are spaces unoccupied by soil material. Soil micromorphologists distinguish between various types of voids, according to their shape and arrangement. Moreover, in soil microscopy, voids between clay particles are not taken into account as they are below the resolution of the optical microscope.


#### **File 18: Morphology of Voids I**

Voids are spaces unoccupied by soil material. Soil micromorphologists distinguish between various types of voids according to their shape and arrangement. Once their nature is identified, voids can be classified according to their morphology.


#### **File 19: The Morphology of Voids II**

Voids are spaces unoccupied by soil material. Soil micromorphologists distinguish between various types of voids, according to their shape and arrangement. Once their nature is identified, voids can be categorized according to their morphology.


#### **File 20: Microstructure I**

Microstructure is a term used to describe the relationship between the solid and the non-solid phases of the soil. It is defined using the morphologies of aggregates and voids, degree of separation of aggregates, as well as the relationships between voids, aggregates, and mineral grains. It is obvious that soils display different types of microstructure according to the magnification used during observation. Therefore, a choice must be made for the description, as this concept is supported by a comprehensive approach to the thin section.

*Captions from upper left corner to lower right corner. All microphotographs in PPL.*


#### **File 21: Microstructure II**

Microstructure is a term used to describe the relationship between the solid and the non-solid phases of the soil. It is defined using the morphologies of aggregates and voids, degree of separation of aggregates, as well as the relationships between voids, aggregates, and mineral grains. It is obvious that soils display different types of microstructure according to the magnification used during observation. Therefore, a choice must be made for the description, as this concept is supported by a comprehensive approach to the thin section.

*Captions from upper left corner to lower right corner. All microphotographs in PPL if not otherwise specified.*


**Open Access** This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http:// creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution, and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

## Chapter 3

#### **Basic Components**

#### **File 22: Mineral and Organic Constituents**

Mineral and organic constituents belong to the basic components observed in soil thin sections. They can appear, for instance, as large rock fragments, or single minerals as sand grains; they can constitute large areas of micromass formed by clay minerals or display parts of plant roots or leaf fragments, i.e. organic material. These constituents comprise the body of the soil itself, and in soil micromorphology, they belong to the groundmass, as well as the material constituting the pedofeatures (see "File 9"). Two types of basic components are recognized by Stoops (2003, 2021), those recognizable at the magnifications of the optical microscope and those which are not. Stoops (2003, 2021) pointed out the problem of the optical microscope resolution and the thickness of conventional thin sections. Indeed, it is preferable not to have a standard size limit between coarse and fine materials. Consequently, there are three main types of basic components: the coarse mineral constituents, the fine mineral phase, and the organic matter-related constituents.

After a description of the sorting and shape of coarse grains, five sections present the main rocks encountered in soils. During their weathering phase, rocks can free mineral grains in the soil environment, and this is illustrated in five other sections. Three sections of rocks show the large diversity of the micromass and the other constituents of the groundmass. Some minerals do not originate from rocks but from living organisms, such as plants, bacteria, fungi, and animals: they are known as "biominerals" and three sections report the most common of them. Organic matter plays a fundamental role in soils and it leaves many traces of its impact at the microscale: three sections describe its various characteristics. Finally, soils were the foundations of all civilizations: they often contain the traces of humankind, which are called anthropogenic features. These are illustrated by two sections.

The diversity of constituents, from minerals to organic or anthropogenic features. All microphotographs are in PPL.

#### **File 23: Particle Size and Sorting**

The proportions of coarse and fine materials, according to their size, their degree of sorting, and their shape, constitute the fundamental parameters related to the soil texture in thin sections. All these terms are currently used in sedimentary petrography to describe terrigenous clastic sedimentary rocks; they are also used in soil science, as far as physical soil properties are concerned. Moreover, regarding particle sizes, it must be stressed that it is difficult to measure the sizes of constituents in thin sections, as they depend on the orientation of the object and its cross-cut plane in respect to the thin section surface.

*Captions start with the ternary plot at the top. Round images below the ternary plot are listed from the upper left corner to the lower right corner.*


#### **File 24: Shape of Grains: Equidimensionality**

Equidimensionality refers to the way particle sizes are organized regarding the three perpendicular dimensions of space and how equal they are. However, particle shapes can only be described according to two dimensions in thin sections; therefore, the real three-dimensional morphology of a particle must be deduced or inferred very carefully, because it depends on the orientation of the object and its cross-cut plane in respect to the thin section surface.


#### **File 25: Shape of Grains: Roundness and Sphericity**

The roundness of a particle is determined by the sharpness of its edges and corners, independently of the shape of the particle itself. The sphericity of a particle is determined by its overall form, independently of the sharpness of its edges and corners. Both properties are commonly evaluated by means of visual estimation charts, even if today, image processing software can automatically generate parameters describing the roundness and sphericity of individual particles (see "File 77").

*Captions start with a visual estimation chart at the top. Then, they are listed from upper left corner to lower right corner.*

1. Visual estimation chart of both roundness and sphericity, redrawn from Powers (1953). Six classes of roundness and two classes of sphericity are provided. In the original work of Powers (1953), the particles were modelled from clay to make possible the addition of details like shape, sphericity, and roundness of particles. Many other charts have been drawn since, but whatever the type, they all are based on the same approach as Powers (1953); they usually add some intermediate steps in the variability of parameters. The roundness classes of Powers (1953) are based on a specific ratio ρ = *<sup>r</sup> <sup>R</sup>*, where *r* is the radius of curvature of the largest inscribed circle and *R* is the radius of the smallest circumscribing circle. The ratio's values range from the "very angular" to the "well rounded" classes, as follows: 0*.*12 to 0*.*17, 0*.*17 to 0*.*25, 0*.*25 to 0*.*35, 0*.*35 to 0*.*49, 0*.*49 to 0*.*70, and 0*.*70 to 1. Based on Wadell's work (Wadell 1932), Krumbein (1941) proposed to estimate the sphericity by 1*/*<sup>3</sup>

calculatingΨ = *bc a*2 , where *a*, *b*, and *c* are the long, intermediate, and short axis dimensions (respectively) of the particle. Today, quantitative image processing automatically allows particles to be selected and shape parameters to be calculated (Heilbronner and Barrett 2014).


#### **File 26: Basalt, Granite, and Gabbro**

It is very common to observe large pieces of fragmented rocks (lithoclasts) in soil thin sections. The recognition of their texture and nature is therefore important as they emphasize the role of soil parent material or can be the result of reworking of an observed soil horizon, indicating an allochtonous origin of the soil material. This section describes three common igneous rocks, i.e. basalt, granite, and gabbro.


#### **File 27: Schist, Gneiss, and Amphibolite**

Some large pieces of lithoclasts in soil thin sections originate from metamorphic rocks. The recognition of their texture and nature is therefore important as they emphasize the role of soil parent material or can be the result of reworking of an observed soil horizon, indicating an allochtonous origin of the soil material. This section describes four common metamorphic silicate rocks, i.e. schist, gneiss, amphibolite, and greenschist.


#### **File 28: Quartzite and Marble**

Some large lithoclasts in soil thin sections originate from metamorphic rocks. The recognition of their texture and nature is therefore important as they emphasize the role of soil parent material or can be the result of reworking of an observed soil horizon, indicating an allochtonous origin of the soil material. This section describes two common rocks that result from the metamorphism of former sedimentary rocks, i.e. quartzite and marble.


#### **File 29: Calcium-Bearing Sedimentary Rocks**

Calcium is the fifth most abundant element on Earth. It is a major compound of numerous sedimentary rocks. Deciphering its origin remains a fundamental issue in soil science, as calcium is a crucial element in many pedogenic processes and biogeochemical pathways (Rowley et al. 2018). Although calcium is incorporated in many structural formulae of silicates, its supply from calcium-bearing sedimentary rocks largely prevails in soil development.


#### **File 30: Sand and Sandstone**

Sands are usually composed by loose detrital particles of rock fragments between 0.05 and 2 mm. Commonly, quartz grains predominantly comprise sands at the surface of continents. During diagenesis, sands undergo hardening by cementation, forming sandstones. Cements can have various mineralogical compositions, from silica to calcium carbonate, from iron oxyhydroxides to sulphates.


#### **File 31: Mineral Grains in the Soil I: Quartz and Chalcedony**

Siliceous grains include quartz, its various polymorphs, and amorphous to cryptocrystalline siliceous minerals, for example chalcedony in chert. In volcanic material, siliceous grains can appear as cristobalite or tridymite.


#### **File 32: Mineral Grains in the Soil II: Feldspar and Mica**

Feldspars are tectosilicates commonly found in igneous and metamorphic rocks (see "File 26"). They are characterized by two mineral families: the K-feldspars and the plagioclases, which form a continuous solid solution with various amounts of sodium and calcium, from albite (a sodium feldspar) to anorthite (a calcium feldspar). During weathering, calcium, sodium, and potassium ions are freed in the soil solution, and feldspar partially transforms into clays and*/*or oxyhydroxides. Micas are phyllosilicates frequently associated with granite and granodiorite but also with metamorphic rocks, such as schist and gneiss (see "File 26" and "File 27"). Muscovite is frequently observed as grains in soils, whereas biotite is rarer, as it is easily weathered and transformed into clay. This difference between the two micas is related to their structural chemical formula, the aluminium in muscovite being much more refractory to weathering than the magnesium and iron in biotite.


#### **File 33: Mineral Grains in the Soil III: Inosilicates and Nesosilicates**

Inosilicates are formed of interlocking chains of silicate tetrahedra and include two main groups of minerals: pyroxenes, as single chain silicates, and amphiboles, as double chain silicates. They are commonly igneous rock-forming minerals but can also be associated with high-temperature metamorphic rocks. In nesosilicates, the silicate tetrahedra are isolated and bound to each other by ionic bounds, making their structure particularly dense, providing them some resistance to weathering. Olivines (minerals found in high-temperature igneous rocks) and garnets (minerals prevalent in metamorphic rocks) form two common members of nesosilicates. Both of these rock-forming silicate groups, inosilicates and nesosilicates, can be observed in soils as residual mineral grains in the coarse fraction.


#### **File 34: Mineral Grains in the Soil IV: Carbonates**

Carbonate minerals are common features of soils. They can be either inherited from the carbonate parent material of the soil (see "File 29" for some examples) or precipitated as secondary pedogenic features (see e.g. "File 72"). In this section, carbonate grains found in soils are inherited from the bedrock. These elements in the soil coarse fraction constitute lithoclasts and not pedofeatures. Carbonate lithoclasts in soils are usually inherited from three main types of rocks: limestones, marls, and dolomites.


#### **File 35: Mineral Grains in the Soil V: Chlorides and Sulphates**

Although many inherited chlorides and sulphates could have been easily dissolved during weathering, some soils can preserve their clasts or imprints. They must not be interpreted in terms of pedogenic processes when they are inherited from the bedrock. It is why their recognition as lithoclasts is paramount. This plate shows examples of a chloride (halite) and three different types of sulphate: barite, anhydrite, and gypsum. In this plate, all these minerals are inherited from the bedrock.


#### **File 36: Biominerals I**

Stoops (2003, 2021) defines biominerals as inorganic residues of biological origin. They include fragments of internal or external skeletons of animals, as well as direct or indirect mineral products of organism metabolism—for more details, see Mann (2001) and Skinner and Ehrlich (2017). Phytoliths are produced in specific plant cells, in intercellular spaces, or associated with cell walls Stoops (2003). Calcium oxalate druses are aggregations of crystals with a roughly overall spherical shape (Baran and Monje 2008), and they also originate from plants. Other forms of oxalate crystals exist, such as equant or needle-shaped morphologies, but both can be associated with plants and fungal filaments (Verrecchia et al. 1993). These minerals indicate the presence of organisms, even if the organic matter has been totally decayed.


#### **File 37: Biominerals II**

Stoops (2003, 2021) defines biominerals as inorganic residues of biological origin. They include fragments of internal or external skeletons of animals, as well as direct or indirect mineral products of organism metabolism—for more details, see Mann (2001) and Skinner and Ehrlich (2017). This section mainly refers to three types of spherulites: (1) calcitic faecal spherulites result from animal digestive processes; they are more abundant in herbivore dung (Durand et al. 2018); (2) another type of calcitic and radial spherulites are found in desert laminar crusts, likely as a by-product of photosynthetic activity by cyanobacteria (Verrecchia et al. 1995); and (3) in bird and reptile droppings, it is possible to find spherulites, composed of uric acid (Canti 1998). These minerals indicate the presence of former biological activity, even if organic matter is not directly observed.


#### **File 38: Biominerals III**

Stoops (2003) defines biominerals as inorganic residues of biological origin. They include fragments of internal or external skeletons of animals, as well as direct or indirect mineral products of organism metabolism—for more details, see Mann (2001) and Skinner and Ehrlich (2017). Mollusc shells are genetically induced biominerals (Mann 2001). The identification of the molluscs as originating from marine or continental environments is a clue to the nature of the soil parent material. Egg shells and bones also belong to genetically induced biominerals (Mann 2001): both of them are common features of archaeological sites (Durand et al. 2018). Finally, some clear and small crystalline aggregates are often found in temperate soils. In thin section, they appear as calcitic spheroids. They are usually formed by earthworms as metabolic by-products in their casts (Durand et al. 2018; Becze-Deak et al. 1997).


#### **File 39: Anthropogenic Features I**

Many types of features in soils can be directly related to anthropogenic activities. In archaeological sites, their presence is obvious, but they can also be encountered in "natural" soils, providing evidence of the incidental presence of humankind (Nicosia and Stoops 2017). Pottery fragments are commonly found in archaeological sites. Chunks of brick can be present in more recent anthropogenic soils. Moreover, not only can artefacts be found in soils, but also secondary chemical deposits, such as amorphous phosphate or vivianite crystals. These deposits are frequently associated to reducing environments enriched in organic matter as, for instance, cesspits and latrines.


#### **File 40: Anthropogenic Features II**

Many types of features in soils can be directly related to anthropogenic activities (Nicosia and Stoops 2017). At archaeological sites, their presence is obvious, but they can also be encountered in "natural" soils. Indeed, a fire can be triggered by nature (e.g. summer forest fires or lightning strikes) or by humans. In this section, the features shown are related to anthropogenic activities induced by fire, i.e. charcoal, ashes, heated bones, and heated rock fragments.


#### **File 41: Organic Matter I**

Organic matter is a common feature of soils worldwide. Soil organic matter includes remains of all plant parts, as well as small animals (insects, arthropods, etc.), fungi, and bacteria. Organic horizons are characterized by their dark colour caused by the melanization (darkening) of the soil organic matter as well as the formation of specific organic molecules. Plants are mainly composed of lignin and cellulose, giving some organic material a birefringence belonging to the first order colours in XPL. In this section, fungal features are described as well as plant material from leaves to roots.


#### **File 42: Organic Matter II**

Roots are the most common organic residues observed in soils. Roots not only appear differently depending on the angle at which they were cut (see "File 41"), but they can also be differentiated according to their preservation or decay. Three examples of similar root sections are given for three different ways of decaying and preservation. In addition, it is possible to find a biogenic product, starch, preserved in soils at certain locations, e.g. in arid zone soils.


#### **File 43: Humus**

Humus forms result from decomposed organic matter lying at the surface of the soil, or present in the uppermost 30 cm. It mainly consists of combinations of Oi, Oe, Oa, and A horizons (IUSS and Working-Group-WRB 2014). The state of preservation and decomposition of plant tissues allows the type of humus form to be recognized. Humus forms are also often associated with earthworm casts and faecal pellets of small animals. A progression from litter to A horizon is presented in this section made from thin sections from a folic Umbrisol and a calcaric Leptosol, Côte de Ballens, Jura Mountains, Switzerland.

*Captions from upper left corner to lower right corner. All views are in PPL.*


#### **File 44: Micromass**

According to Bullock et al. (1985), micromass is a general term used to denote the finest material of the groundmass. Stoops (2003, 2021) describes the micromass as being characterized by the presence of crystalline or amorphous clay minerals, associated with oxyhydroxides or not, amorphous organic matter, and possibly the presence of small crystals of calcite (i.e. micrite) or mica. Micromass can be described using its colour, its transparency (i.e. its limpidity), and the interference colours (i.e. its bfabric). Limpidity ranges from limpid to opaque, with intermediate states such as cloudy, speckled, and dotted. This section presents examples or micromass colours and limpidity, which have to be observed in PPL. In addition, the next two sections show examples of b-fabrics observed in XPL.


#### **File 45: B-Fabric I**

According to Bullock et al. (1985), micromass is a general term used to indicate the finest material of the groundmass. Stoops (2003, 2021) describes the micromass as being characterized by the presence of crystalline or amorphous clay minerals, associated with oxyhydroxides or not, amorphous organic matter, and possibly the presence of small crystals of calcite (i.e. micrite) or mica. Micromass can be described using its colour, its transparency (i.e. its limpidity), and the interference colours (i.e. its bfabric). The b-fabric describes "the origin and patterns of orientation and distribution of interference colours in the micromass" (Bullock et al. 1985). This section shows examples of thin sections observed only in XPL.


#### **File 46: B-Fabric II**

According to Bullock et al. (1985), micromass is a general term used to indicate the finest material of the groundmass. Stoops (2003, 2021) describes the micromass as being characterized by the presence of crystalline or amorphous clay minerals, associated with oxyhydroxides or not, amorphous organic matter, and possibly the presence of small crystals of calcite (i.e. micrite) or mica. Micromass can be described using its colour, its transparency (i.e. its limpidity), and the interference colours (i.e. its bfabric). The b-fabric describes "the origin and patterns of orientation and distribution of interference colours in the micromass" (Bullock et al. 1985). This section shows examples of thin sections observed only in XPL, displaying the presence of elongated areas in which clays are approximately simultaneously extinct.

*Captions from upper left corner to lower right corner.*


**Open Access** This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http:// creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution, and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

## Chapter 4

#### **Pedogenic Features**

#### **File 47: Imprints of Pedogenesis**

From a historical point of view, soil micromorphology was first used in order to decipher the expressions of pedogenic processes at the microscale (Kubiëna 1938). In the preceding chapters, the Atlas listed a series of descriptive tools to help with the identification of objects. This chapter deals with specific pedofeatures encountered in a large diversity of soils and directly related to pedogenic processes. Pedological features (Brewer 1964) or pedofeatures (Bullock et al. 1985) are "discrete fabric units present in soil materials that are recognizable from an adjacent material by a difference in concentration in one or more components or by a difference in internal fabric" (Stoops 2003, 2021). In Stoops (2003, 2021), pedofeatures are subdivided into two categories: matrix pedofeatures and intrusive pedofeatures. Matrix pedofeatures can be subdivided according to their relationship with the groundmass (depletion, impregnative, and fabric pedofeatures) and to their morphology (hypocoatings, quasicoatings, matrix infilling, intercalation, and matrix nodules). Regarding the intrusive pedofeatures, they include coatings, infillings, crystals and crystal intergrowth, intercalations, and finally nodules. The proposed nomenclature of this chapter is based on the nature and morphology of the pedofeatures, simplified from Bullock et al. (1985).

Examples of pedofeatures from left to right: a polygenetic nodule (XPL), hypo- and quasicoatings (PPL), clay infilling (PPL), infilling of needle-fibre calcite (XPL), and pellets (PPL).

#### **File 48: Iron- and Manganese-Bearing Nodules**

Nodules are defined as roughly equidimensional pedofeatures that are not related to natural surfaces or voids and that do not consist of single crystals. From a theoretical point of view, nodules can be regarded as matrix impregnative or intrusive pedofeatures (Stoops 2003). This plate presents iron-bearing nodules, and according to Bullock et al. (1985), they can be classified as amorphous or cryptocrystalline pedofeatures based on their internal fabric and external morphology. The chemical nature of nodules is often confirmed using an electron microprobe; for example, element mapping frequently shows the association of iron and manganese (see "File 7").


#### **File 49: Carbonate Nodules**

Nodules are defined as roughly equidimensional pedofeatures that are not related to natural surfaces or voids and do not consist of single crystals (Stoops 2003). From a theoretical point of view, nodules can be regarded as matrix impregnative or intrusive pedofeatures (Stoops 2003). This plate presents carbonate nodules, and according to Bullock et al. (1985), they can be classified as crystalline pedofeatures based on their internal fabric and external morphology. Moreover, the size of carbonate crystals forming the nodule (i.e. micrite, microsparite, or sparite) is also a pertinent attribute of such pedofeatures.


#### **File 50: Polygenetic Nodules**

Polygenetic nodules are either nodules composed of multiple generations of cortical layers or products of different pedogenetic phases. A special type of polygenetic nodule is associated with perlitic crusts. These crusts are made of multiple polygenetic nodules, also called ooids (Durand et al. 2018), of various sizes in a monic to close porphyric c/f related distribution and almost always associated with carbonate laminar crusts.


#### **File 51: Nodules: Morphology and Border Shape**

Nodules can be characterized by their specific external morphologies. As pedofeatures, nodules also have spatial relationships with the groundmass surrounding them; this relationship is illustrated by the shape of nodule's border.


#### **File 52: Nodules: Orthic, Anorthic, and Disorthic**

Nodules can be formed in situ, reworked to varying degrees, or inherited from the parent material. In order to identify their origin, Stoops (2003, 2021) suggests the classification proposed by Wieder and Yaalon (1974). When nodules are inherited from the parent material or are clearly allochthonous, they are called *anorthic*. If nodules are formed *in situ* and do not show any sign of reworking, they are considered as *orthic*. If they were locally displaced inside the soil, they are qualified as *disorthic*.

*Captions start with the sketch in the central left column. Then, the microphotographs are described clockwise around the sketch, starting from the upper left corner to the lower left corner.*


#### **File 53: Crystals and Crystal Intergrowths**

Crystals and crystal intergrowths are individual or clusters of crystals, which are precipitated inside the soil groundmass. Such crystals are not inherited from the parent material but are the product of pedogenic processes. According to Stoops (2003, 2021), crystal intergrowths are subdivided based on their distribution and/or orientation pattern, and according to Bullock et al. (1985), they can be classified as crystalline pedofeatures based on their internal fabric and external morphology.


#### **File 54: Impregnations**

One of the descriptive parameters of matrix pedofeatures includes the degree of impregnation. Nodules are sometimes regarded as matrix pedofeatures (see "File 48" and "File 52"). Four degrees of impregnation are proposed by Stoops (2003, 2021) according to the amount of recognizable components of the groundmass, i.e. regarding the purity of the feature: weakly impregnated, moderately impregnated, strongly impregnated, and pure. The first four microphotographs refer to a carbonate environment, whereas the last four to aluminosilicate- and iron-rich settings.


#### **File 55: Depletions**

Depletion pedofeatures are defined as lower concentrations of a given component of the micromass, e.g. calcite or iron oxyhydroxides (Bullock et al. 1985; Stoops 2003, 2021). The loss of matter can be related to either dissolution, e.g. in a carbonate environment, or redox processes, e.g. in iron-rich environments. The mobilized ions are then translocated or leached inside or outside the profile, respectively.


#### **File 56: Coatings with Clays I**

Coatings are defined as intrusive pedofeatures that coat natural surfaces of voids, grains, or aggregates inside soils (Stoops 2003, 2021). Coatings must not be confused with infillings (see "File 61"). Coatings are constituted by various material types, i.e. clays, and coarse, amorphous, or crystalline material. This section shows coatings formed by clays, one of the earliest pedogenic features recognized in thin sections. *In situ* clay coatings are diagnostic features of leaching processes and are also used in soil classifications. Clay coatings are described according to their colour, the presence or absence of laminations, their thickness, and their grain size (i.e. they can be called textural pedofeatures).


#### **File 57: Coatings with Clays II**

Coatings are defined as intrusive pedofeatures that coat natural surfaces of voids, grains, or aggregates inside soils (Stoops 2003, 2021). This section shows peculiar characteristics of coatings formed by clays associated to either reworking, massive deposition, or effects of waterlogging. Moreover, clay coatings must not be confused with clay neoformation in saprolite cracks, a case illustrated in the last two pictures.


#### **File 58: Micropans, Coarse Coatings, Cappings, and Crusts**

Coatings are defined as intrusive pedofeatures that coat natural surfaces of voids, grains, or aggregates inside soils (Stoops 2003, 2021). In terms of morphologies, coatings can be subdivided into several types, such as the typic and crescent ones shown in "File 56" and "File 57". Micropans, crusts, and cappings are illustrated in this section. These types are often composed of material coarser than clay; consequently, this section also contains examples of coarse coatings.


#### **File 59: Hypocoatings and Quasicoatings: Amorphous**

The difference between coatings, hypocoatings, and quasicoatings is the location of the material with respect to the internal soil surface. Hypocoatings refer to an accumulation of matter impregnating the soil groundmass directly adjoining the void edge (the internal soil surface). Quasicoatings are not in direct contact with the void border: there is a rim of soil groundmass material between the void and the quasicoating pedofeature. Because of their impregnative nature, hypocoatings and quasicoatings are mainly amorphous (this section) or crystalline ("File 60"). "Amorphous" refers to isotropic properties of iron and manganese oxyhydroxides, which mainly form these kinds of pedofeatures; according to Bullock et al. (1985), they can be regarded as amorphous or cryptocrystalline pedofeatures.

*Captions start with the uppermost sketch, followed by the microphotographs from upper left corner to lower right corner.*


#### **File 60: Coatings and Hypocoatings: Crystalline**

The difference between coatings and hypocoatings is the location of the material in respect to the internal soil surface. Coatings are intrusive pedofeatures that cover natural surfaces of voids, grains, or aggregates. Hypocoatings refer to an accumulation of matter impregnating the soil groundmass directly adjoining the void edge (the internal soil surface). This section includes various types of such crystalline pedofeatures (Bullock et al. 1985) that are related to void edges.


#### **File 61: Mineral Infillings**

Infillings are formed by soil material or some fraction of it, which fills any void other than packing voids (Stoops 2003, 2021). These infillings are formed by mineral material originating from either biological (see "File 62") or physicochemical processes. This plate shows examples of mineral infillings, which can be coarse or fine and of different mineralogical natures. They are termed textural or crystalline pedofeatures according to their composition.


#### **File 62: Mineral Infillings of Biological Origin**

Infillings are formed by soil material or some fraction of it, which fills any void other than packing voids (Stoops 2003, 2021). These infillings are formed by mineral material originating from either biological (see "File 61") or physicochemical processes. This plate shows examples of biomineral infillings. They are termed crystalline pedofeatures according to their composition.


#### **File 63: Pedoturbations**

Pedoturbation is defined as any kind of physical mixing of soil material accomplished by the following mechanisms: shrinking and swelling of clays, freeze–thaw activity, and bioturbation by animals or plants. It is not because the soil material is mixed that it becomes homogenized (Schaetzl and Thompson 2015). However, even if some homogenization seems obvious at the macroscale, at the microscale, the effects of pedoturbation are always visible because of the imprint of the various processes. In addition, in Stoops (2003), most of the pedoturbations are included in fabric pedofeatures (belonging to matrix pedofeatures), which are "recognizable from the groundmass because of difference in fabric only".


#### **File 64: Faecal Pellets**

Sometimes referred to as "excrements of the mesofauna" (Stoops 2003, 2021), faecal pellets (in the sedimentological sense of the word) do not only belong to a special type of pedofeature but can also create granular and/or vermicular microstructures (see "File 20" and "File 21"). They can form infillings as well. The faecal pellet's shape can refer to specific mesofaunas, as listed in Stoops (2003, 2021) and Bullock et al. (1985).


#### **File 65: Dung and Vertebrate Excrements**

Dung and excrements of large animals are mainly of interest to archaeological micromorphology (Nicosia and Stoops 2017), whereas faecal pellets can be observed in both natural soils and archaeological settings. Regarding excrements, they are characterized by different external shapes, colours, basic constituents, and internal fabrics, depending on the genera of the animals (Stoops 2003).


#### **File 66: Composite Pedogenic Features**

Pedofeatures made up of several parts or elements (i.e. composite) encompass compound and complex pedofeatures, as defined by Stoops (2003). They consist of a mixture of two or more pedofeatures resulting from different pedogenic processes, either contemporaneous or successive. If each single pedofeature lies side by side, they are defined as juxtaposed, whereas if they overlap, pervade, or affect one another, they are considered to be superimposed.


#### **File 67: Uncommon Features**

The list of uncommon features encountered in soil thin sections could be very lengthy. In this section, only eight have been selected and concern specific minerals, forms of organic matter, and finally some micromorphological effects produced by termites and tropical trees. The examples chosen are sometimes confused with other features.

*Captions from upper left corner to lower right corner.*


**Open Access** This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http:// creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution, and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

Chapter 5

#### **Pedofeatures Associated to Soil Processes**

#### **File 68: Pedofeatures and Soil Processes**

As stipulated by G. Stoops, "the aim of micropedology is to contribute to solving problems related to the genesis, classification and management of soils, including soil characterization in palaeopedology and archaeology. The interpretation of features observed in thin sections is the most important part of this type of research, based on an objective detailed analysis and description" (Stoops et al. 2018). To answer such questions, two major books contributed to the comparative knowledge necessary to tackle this objective: the first one was published in 1985 and used micromorphology to distinguish between different classes of soils (Douglas and Thompson 1985); the second one is an extensive guide of more than 1000 pages to the interpretation of micromorphological features encountered in thin sections of soil (Stoops et al. 2018). The aim of this Atlas is neither to be a substitution for these books nor a way to enter directly into the interpretation of soil genesis and classification. Nonetheless, this chapter presents the imprints of major soil processes that can be easily deduced from specific features observed in thin sections. These processes involve the dynamics of (a) clay, both translocation and swelling, (b) water, such as waterlogging, evaporation, and its role as ice and frost, (c) carbonate, gypsum, and iron oxyhydroxides, and finally (d) biogeochemical reactions within the solum.

Examples of micromorphological expressions due to specific pedogenic processes: vertic material (XPL), a hydromorphic feature (PPL), precipitation of sulphate in an arid environment (XPL), clay neoformation (XPL), the influence of podzolization (PPL).

#### **File 69: Clay Dynamics I: Translocation**

Translocation refers to the mechanical process of displacing clays (or other material) in their dispersed state, i.e. in the form of isolated particles (Schaetzl and Thompson 2015). This process is related to vertical or lateral water movements in the soil profile. It is one of the first observed processes in thin section during the last century. This process can affect a large variety of soils, changing the associated features (textural pedofeatures; see "File 56", "File 57", "File 58" and "File 61") in terms of grain size and mineralogy. The soil porosity plays a major role in translocation, i.e. in mobilization and sedimentation. In addition, the soil chemistry can also influence the dispersed state of the mineral particles. Finally, climate (including seasonality) has a distinct impact on translocation, as free percolating water is needed to displace the particles.


#### **File 70: Clay Dynamics II: Swelling**

Some soils are characterized by a parent material containing a high proportion of TOT clays. Some clays have the property to shrink and swell depending on soil moisture saturation, leading to a pedogenetic process known as vertisolization and a specific class of soils, i.e. Vertisols (Duchaufour 1977; Legros 2012). Vertisols exhibit distinct characteristics, which are described in this section.


#### **File 71: Water Dynamics**

Water is the main force in pedogenesis. It influences soil dynamics in many ways. In this section, three types of water-driven processes are considered: waterlogging, evaporation, and water in freezing/thawing environments.


#### **File 72: Carbonate and Gypsum Dynamics**

Pedogenic carbonate-rich soils must not be confused with *calcrete*, although this confusion is widespread in the literature. Calcium carbonate redistributions in soils can occur under various climates and are not limited to the semiarid and arid zones. Indeed, large redistributions of *CaCO*<sup>3</sup> are caused by organisms, i.e. bacteria, fungi, roots, and animals (Durand et al. 2018). Many pedogenic carbonates result from the incorporation of soil *CO*<sup>2</sup> (Hasinger et al. 2015) and are not the consequence of a simple dissolution and reprecipitation from a carbonate parent material. Gypsum dynamics necessitate dissolution and reprecipitation of sulphate through evaporation processes. There are some exceptions related to anthropogenic influences, such as acid rain.


#### **File 73: Processes Involving Iron Oxyhydroxides**

Under intense geochemical weathering, oxyhydroxides can be redistributed inside the groundmass (Duchaufour 1998). This process usually turns the micromass red (rubification), which is a common trait of two distinct processes: fersiallitization and ferrallitization (Duchaufour 1977; Schaetzl and Thompson 2015). In addition, due to the strong weathering of primary minerals, clays can form and become the main compound of the micromass. An exhaustive description of mineral weathering at the microscale can be found in Delvigne (1998).


#### **File 74: Biogeochemical Processes I**

During biogeochemical processes, organic matter can combine with mineral compounds to form organomineral complexes that give soils specific properties. In addition, organic matter constitutes a driving force of pedogenesis as it influences the processes of weathering, as well as the transfer of matter inside profiles (Duchaufour 1997). In soil micromorphology, podzolization and andosolization are clearly expressed by specific features. In the case of podzols, horizons display striking micromorphological differences, while in andosols, micromorphological characteristics are found more in the general aspect of the thin section.


#### **File 75: Biogeochemical Processes II**

Brunification is a common biogeochemical process observed in temperate regions, during which clay minerals, iron, and organic matter interact to form clay–humic and clay–iron complexes. In environments with more pronounced contrasts between seasons, another type of biogeochemical process prevails, i.e. the deep incorporation of stable organic matter forming isohumic profiles. Unfortunately, soil micromorphology cannot provide any clear and univocal sets of diagnostic features for such kinds of processes. In this section, only a few examples of micromorphological aspects of soils under brunification and melanization are given.

*Captions from upper left corner to lower right corner.*


**Open Access** This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http:// creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution, and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

## Chapter 6

## **The Future of Soil Micromorphology**

#### **File 76: The Future of Soil Micromorphology**

The advancement of technology opens up new opportunities to soil micromorphology. Although a description using an optical microscope of the fabric and the various constituents of soils will be always necessary to investigate soil evolution, the uncovered thin section leaves soil material on which analyses can be performed. Since the 1970s, it was possible to observe thin sections at high resolution with the scanning electron microscope in its backscattered electron mode (see "File 7"). It was also possible to generate chemical images with electron microprobes. But these conventional techniques, as well as new ones, greatly improve the study of matter interactions in soils, not only by enhancing the spatial resolution with incredible precision but also by providing chemical and mineralogical images, which substantially increased the accuracy of micromorphological diagnostics. By coupling morphological and chemical approaches, including stable isotope imaging in soil material, the future of soil micromorphology will undoubtedly offer new opportunities to solve specific problems, especially in the field of organomineral interactions in soils. It is wise to say that soil micromorphology, with its analytical and holistic approaches, will make it possible to build the necessary solid foundations needed for investigations that are increasingly oriented towards nanoscale objects: it will remind us that the trees should not hide the forest.

Cockpit of the microXAS Beamline at the Swiss Light Source, Paul Scherrer Institute, Villigen PSI, Switzerland.

#### **File 77: Beyond the Two Dimensions**

Based on density variation and X-ray attenuation, X-ray microtomography makes it possible to visualize the organization of voids and particles of different natures in a soil volume. Another tool, electron backscatter diffraction (EBSD), can be used to detect the crystallographic axes of minerals in a thin section of soil. Finally, a device such as the QEMSCAN opens the avenue of quantitative analysis of minerals in thin sections of soil.


#### **File 78: The Prospect of Chemical Imaging**

It must not be forgotten that uncovered thin sections are still a natural soil sample. Minerals and organic matter remain accessible for measurements, and this is particularly true with modern instruments, with which it is possible to map the chemical and mineralogical compositions of the various components forming the soil. This section provides a few examples of chemical measurements made on sections or small soil objects, performed with different instruments.

*Captions from upper left corner to lower right corner.*


**Open Access** This chapter is licensed under the terms of the Creative Commons Attribution 4.0 International License (http:// creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution, and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

The images or other third party material in this chapter are included in the chapter's Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the chapter's Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

© The Author(s) 2021 E. P. Verrecchia, L. Trombino, *A Visual Atlas for Soil Micromorphologists*, https://doi.org/10.1007/978-3-030-67806-7

#### **Chemical Formulae of Some Minerals Observed in Soils**


Appendix A

## **Errors and Pitfalls I**

During thin section fabrication, some artefacts can be inadvertently generated, forming "features" that must be differentiated from true natural traits of soils. This section and the following one give some examples (not an exhaustive list of possible errors and pitfalls) of artefacts of different origins.


## **Errors and Pitfalls II**

During the thin section fabrication, some artefacts can be inadvertently generated, forming features that must be differentiated from true natural traits of soils. This section and the former one give some examples (not an exhaustive list of possible errors and pitfalls) of artefacts of different origins.









## Appendix D

#### **How to Describe a Thin Section**

The description of a soil thin section can be extremely time consuming. Therefore, a good protocol will save a lot of time. This section introduces a succession of steps that can help to organize the thin section description and proposes two ways to comprehensively present the data for reports or publications. The first is in a table for listing the pertinent information, which can be processed with any spreadsheet software (Bullock et al. 1985); obviously, such a checklist needs to be re-created for each soil and site type. The second is a graphical summary of results, introduced by Kemp (1985). Both approaches are complementary and could be provided in a document.

The following steps can be used to make a preliminary and detailed description of a thin section (see also "File 9"):


*Captions from top to bottom.*


Appendix E

#### **Multilingual List of Useful Micromorphological Terms**

This multilingual lexicon provides the most useful terms that can be applied in soil micromorphology in four different languages, i.e. English, French, Italian, and German. The idea of a lexicon has been borrowed from Georges Stoops, who proposed one as early as 1986 (Stoops 1986). A new and up-todate list was compiled in 2017 by Georges Stoops and different authors in 19 different languages (www. isric.online/explore/ISRIC-collections/micromulti). This list concentrates exclusively on the vocabulary used in this Atlas and, therefore, is not exhaustive compared to Stoops (2003, 2021). Some translations are not the same in the list available on the cited website and in this Atlas, due to some corrections.



#### E Multilingual List of Useful Micromorphological Terms 167



#### **References**


© The Author(s) 2021

E. P. Verrecchia, L. Trombino, *A Visual Atlas for Soil Micromorphologists*, https://doi.org/10.1007/978-3-030-67806-7


References 171


#### **Index**

#### **A**

Accommodation, 31 Acicular, 47, 133 Aeolian, 59 Aggregate, 25, 29, 31, 35, 39, 41 accommodation, 31 angular blocky, 29, 41 crumb, 29, 35, 39, 85 granular, 121 granule, 29, 39, 85 morphology, 29 plate, 29, 41, 141 prism, 29, 141 separation degree, 31 subangular blocky, 29, 33, 35, 41 Albite, 63 Alizarine, 15 Allophanes, 89, 147 Amorphous, 51, 61, 65, 77, 87, 95, 111, 117 Amphibole, 51, 53, 65, 89 hornblende, 53 Amphibolite, 53 Analyser, 9, 15 Andosolisation, 147 Angular, 49 Anhydrite, 69, 143 Anorthite, 63 Anthropogenic soil, 77 Apatite, 75 Aragonite, 75, 133 Arenic, *see* Grain size Argilliturbation, 137, 145 Ash, 51, 79

#### **B**

B-fabric, 15, 87, 89, 91, 137, 139 bistrial, 89 circular striated, 91, 121 concentric striated, 91 cross-striated, 91 crystallitic, 89, 139, 143 granostriated, 91

monostriated, 91 parallel striated, 91 porostriated, 91, 125 random striated, 91 speckled, 89 undifferentiated, 77, 89 unistrial, 89 Backscattered electron, 7, 13, 151, 153, 155 Barite, 69 Basalt, 51, 53 Basic components, 43 Basic distribution pattern, 23 banded, 23 clustered, 23 fan-like, 23 interlaced, 23 linear, 23 random, 23 Bioclast, 67 Biomineral, 43, 71, 73, 75, 129 Biospheroid, 75, 127 Biotite, *see* Mica Bioturbation, 69, 125, 137, 149 Birefringence, 15 Bone, 75, 79 Brick, 77 Brunification, 149 Bryozoans, 67

#### **C**

c/f related distribution, 25, 27 chito-gefuric, 27, 61 chitonic, 25, 27, 81, 147 close porphyric, 149 enaulic, 25, 147 gefuric, 25, 147 monic, 25, 137, 147 porphyric, 149 porphyric close, 25, 137 porphyric double-spaced, 27 porphyric open, 25 porphyric single-spaced, 27, 149

© The Author(s) 2021 E. P. Verrecchia, L. Trombino, *A Visual Atlas for Soil Micromorphologists*, https://doi.org/10.1007/978-3-030-67806-7

Calcified root cells, *see* Calcite Calcite, 15, 55, 67, 75, 81, 83, 87, 89, 91, 105, 133, 143 calcified root cells, 83, 119, 123, 133, 143 fan-like, 119, 139 fibrous, 119 micrite, 27, 47, 57, 59, 67, 79, 81, 87, 89, 91, 97, 103, 107, 119, 121, 139 microsparite, 27, 47, 59, 67, 97, 99, 103, 107, 119, 121, 131, 139, 145 needle-fibre, 47, 75, 123, 133, 143 sparite, 55, 57, 59, 67, 97, 99, 107, 119, 121, 131 Calcium carbonate, *see* Calcite Calcium oxalate, *see* Oxalate Calcrete, 143 Capping, 115, 125, 141 Cathodoluminescence, 11 Ceramic, 77 Chalcedony, 57, 61 Chalk, 57 Chamber, 37 Channel, 33, 37, 81, 127 Charcoal, 79, 85 Chert, 79 Chloride, 69, 141 Chlorite, 53 Clay coating, 15, 21, 23, 61, 111, 113, 131 infilling, 23, 131 intercalation, 113 minerals, 21, 25, 27, 43, 77, 79, 87, 89, 91 neoformation, 113 translocation, 137 Clay minerals, 13 Clay-humic complex, 149 Clay-iron complex, 149 Clayic, *see* Grain size Cleavage, 9, 63 Coating, 111, 113, 115, 119 capping, 115, 125 clay, 111, 113, 131, 137 coarse, 111, 115 compound layered, 115 crescent, 111 crust, 115 dusty clay, 115 fragment, 113 laminated, 111, 113 limpid, 111 micropan, 115 non-laminated, 111 typic, 111, 113 Cold cathode, 11 Compositional study, 17 Cone-in-cone, 139 Convoluted fabric, 123, 143 Cross-polarised light, 9, 15 Crust, 115 laminar, *see* Laminar crust perlitic, *see* Perlitic crust

Cryptocrystalline, 61, 65, 95, 117

Crystal, 105 Crystal intergrowth, 105, 133 Cubic, 69

#### **D**

Darkening, *see* Melanisation Depletion, 109, 141, 143 Diatomite, 133 Dolomite, 55, 67, 133 Druse, 71, 75, 129 Dung, 11, 71, 73, 83, 129

#### **E**

Earthworm, 75, 85, 127 EBSD, *see* Electron backscatter diffraction Electron backscatter diffraction, 55, 153 Electron beam, 11 Electron probe micro-analysis, 13, 95, 155 Energy dispersive X-ray spectroscopy, 13, 153 Epidote, 53 Equant, 47 Equidimensionality, 47 Evaporation, 141 Excrements, *see* Faecal pellets large animals, 129 mesofauna, 127 Extinction, 9

#### **F**

Fabric, 17 definition, 19 partial, 21 unit, 21, 23 Faecal pellets, 49, 85, 127 Feldspar, 51, 63 microcline, 51, 63 orthoclase, 51 plagioclase, 51, 53, 63 Ferrallitisation, 145 Ferricyanide, 15 Fersiallitisation, 145 Flint, *see* Chert Fluorescence, 11 Frost, 115, 125, 141 Fungi, 71, 81, 123, 143 filament, 81 sclerotium, 81, 85

#### **G**

Gabbro, 51, 53 Garnet, 53 Gneiss, 53 orthogneiss, 53 paragneiss, 53 Goethite, 87, 105, 111 Grain size, 45, 61 Granite, 51

#### Index 175

Granoblastic, 53 , 55 Graphite, 133 Groundmass, 15 , 17 , 21 , 43 , 87 , 89 , 91 Gypsum, 69 , 121 , 143 Gypsum plate, 57 , 99

#### **H**

Halite, 69 , 141 Heating, 79 Hematite, 13 , 87 , 111 , 113 Hornblende, 53 Humus, 85 Hydromorphism, 109 , 141 Hypocoating, 117 , 119 , 125 , 131 , 141

#### **I**

Iddingsite, 65 Impregnation, 7 , 107 Infilling, 137 crystalline, 121 , 123 faecal pellet, 127 textural, 121 , 131 Inosilicate, 65 Intercalation clay, 113 Intrusive pedofeatures, 93 , 95 Iron, *see* Oxyhydroxide Isohumic, 149 Isometric, 69 Isotropic, 15

#### **J**

Juxtaposed, *see* Pedofeatures

#### **K**

Kaolinite, 13 Kikuchi pattern, 153 Kubiëna box, 5

#### **L**

Laminar crust, 73 , 99 , 143 Laser-ablation ICP-MS, 155 Leaf, 81 Limestone, 57 , 67 oolitic, 57 silicified, 57 Lithoclast, 51 , 53 , 55 , 67 , 123 Loamic, *see* Grain size

#### **M**

Malachite, 59 Marble, 55 Marl, 57 , 67 Matrix impregnative, 97 Matrix impregnative pedofeature, 93 , 95 Melanisation, 81 , 83 , 87 , 149 Mica, 51 , 63 , 87 , 89 , 91 biotite, 51 , 53 , 63 muscovite, 53 , 63 sericite, 53 Michel-Lévy table, 15 Micrite, *see* Calcite Microcline, *see* Feldspar Microcodium, 11 , 133 , 153 Micromass, 11 , 17 , 21 , 25 , 27 , 43 , 47 , 49 , 51 , 79 , 87 , 89 , 91 Micropan, 115 Microscope, 9 , 15 Microsparite, *see* Calcite Microstructure, 39 , 41 angular, 41 chamber, 39 channel, 39 complex, 41 crack, 39 crumb, 39 granular, 39 , 79 lenticular, 41 , 141 massive, 41 platy, 41 spheroidal, 41 spongy, 39 subangular, 41 vermicular, 41 vesicular, 39 , 51 vughy, 39 Mollusc, 75 Monomorphic, 147 Muscovite, *see* Mica, 63

#### **N**

NanoSIMS, 155 Needle-fibre calcite, *see* Calcite Nesosilicate, 65 Nodule, 13 , 95 , 97 , 131 , 139 aggregate, 95 , 139 alteromorphic, 95 anorthic, 103 border, 101 carbonate, 97 concentric, 95 , 97 dendritic, 95 disorthic, 103 geodic, 95 , 97 , 107 iron, 13 , 95 matrix, 21 morphology, 101 nucleic, 95 , 97 orthic, 103 polygenetic, 99 siliceous, 99 spetaric, 97 typic, 95 , 97 , 107

#### **O**

Oblique incident light, 11

OIL , seeOblique incident light11 Olivine, 51, 65, 89 Ooids, 99 Opal, 71 Organic matter, 11, 15, 17, 25, 35, 43, 73, 81, 83, 85, 87, 89, 91 Orthoclase, *see* Feldspar Oxalate, 71, 81, 129, 133 Oxyhydroxide, 13, 15, 21, 25, 27, 59, 67, 87, 89, 91, 99, 107, 117, 131, 133, 139, 145

#### **P**

Packing void complex, 35 compound, 33, 35 simple, 33, 35, 59, 61 Palisade fabric, 133 layer, 75 Papula, 113 Particle shape, 49 Pattern basic distribution, *see* Basic distribution pattern definition, 23 Peat, 87, 133 Pedofeatures, 19, 67, 93 amorphous, 95, 117 compound, 117, 131 crystalline, 97, 105, 119, 121, 123 depletion, 109, 131, 141 fabric, 125 intrusive, 17, 93, 97, 111, 113, 115, 119, 139 juxtaposed, 117, 131 matrix, 17, 93, 117, 119, 125, 149 superimposed, 117, 131 textural, 111, 113, 115, 121, 137 Pedoturbation, 121, 125 Peds, 29, 31, 33, 35 Perlitic crust, 99 Phenocryst, 51, 55 Phosphate, 11, 57, 77, 119, 121, 131 Phytolith, 71, 129 Plagioclase, *see* Feldspar Planar, 47 Plane polarised light, 15 Plane-polarised light, 9 Planes, 33 curved, 35 desiccation, 141 straight, 35, 141 zigzag, 35, 125, 133 Plant remains, 71, 79, 85 Pleochroism, 55, 61, 105 Podzolisation, 147 Polarisation, 9, 15 Polariser, 9 Polymorphic, 147 Pottery, 77 PPL, *see* Plane-polarised light Prolate, 47

Pseudomorphosis, 95, 105 Pumice, 51 Purity, 107 Pyroxene, 51, 65

#### **Q**

QEMSCAN, 153 Quartz, 15, 25, 51, 61 Quartzite, 55 Quasicoating, 117, 141

#### **R**

Redox conditions, 109, 141 Refringence, 9, 15 Relief, 9, 63 Retardation, 15 Rock igneous, 51 metamorphic, 53, 55 sedimentary, 57, 59 Root, 47, 81, 83, 109, 125, 127, 141, 143 Rounded, 49 Roundness, 49 Rubification, 145

#### **S**

Sampling, 5 Sand, 59 Sandstone, 59 calcareous, 59 ferruginous, 59 Sapric, 133 Scanning electron microscopy, 13, 47 Schist, 53 greenschist, 53 mica-schist, 53 Sclerotium, *see* Fungi Selective extraction, 15 Sericite, *see* Mica Shape, 45 Shell egg, 75 mollusc, 67, 75 Shrinking, 125 Silica, 99, 119 Siltic, *see* Grain size Slickenside, 121, 125, 139 Sorting, 45 Sparite, *see* Calcite Sphericity, 49 Spherulite calcitic, 73 chalcedony, 61 faecal, 71, 73, 129 uric acid, 73 Stage, 9, 15 Starch, 83 Sulfate, 69, 135, 143

#### Index 177

Superimposed, *see* Pedofeatures Swelling, 125

#### **T**

Termites, 133 , 149 Thin section preparation, 7 size, 7 thickness, 7 , 15 Translocation, 137 , 145 Transmission electron microscopy, 13 Travertine, 57

#### **U**

Uric acid, *see* Spherulite

#### **V**

Vermiculite, 63 Vertisol, 139

Vertisolisation, 139 Vesicle, 35 Vivianite, 77 , 105 , 121 Void, 39 , 41 chamber, 37 channel, 33 , 37 , 81 , 127 , 137 definition, 33 , 35 , 37 packing, 33 , 35 , 61 , 137 plane, 29 , 33 , 35 star-shaped vugh, 37 vesicle, 35 vugh, 37 , 137 Vugh, 37

#### **W**

Waterlogging, 113 , 141 Wavelength-dispersive X-ray spectroscopy, 155

#### **X**

XPL, *see* Cross-polarised light