guide to thin section microscopy - Mineralogical Society of America

Guide to Thin Section Microscopy
Preface
Raith, Raase, & Reinhardt – January – February 2012 2012
Preface to the First Edition
The microscopic investigation of materials such as minerals, rocks, ores, technical and other
synthetic products in transmitted and reflected light remains one of the classic, and to this day
indispensable, mineralogical methods of analysis. Polarized-light microscopy provides a nondestructive
way to identify solid substances (whether crystalline or amorphous) with
relatively high spatial resolution, while the phases can be studied within their textural
framework. It allows an estimate of chemical compositions and provides clues to the history
of formation of the material, using specific textural characteristics (structure, fabric, phase
assemblage, phase relationships, reaction textures). Thus, in many respects polarized-light
microscopy has distinct advantages over bulk-analytical methods that use sample powders for
phase identification (XRD) or for the analysis of chemical composition (XRF, AAS). The
limitations of polarized-light microscopy are obvious where the chemical composition of
complex solid solutions has to be determined, or where the material is too fine-grained to
allow the identification of single phases. Depending on the specific objectives and the nature
of the material to be investigated, a modern study in material science will therefore aim to
combine polarized-light microscopy with complementary non-destructive methods of high
spatial resolution (EMPA, SEM-EDX, TEM).
There are numerous textbooks that provide detailed accounts of the determinative techniques
of polarized-light microscopy as well as the crystal-optical background for examining
transparent amorphous and crystalline phases (glasses, minerals, synthetic substances).
Hence, there is no need for a comprehensive presentation of that material in the following
introduction to mineral determination in thin section. For practical work at the polarized-light
microscope it is sufficient to summarise the necessary facts such that even users without an
in-depth knowledge of mineralogy can follow the instructions. Fundamentals of crystal optics
and crystallography are included only where they are crucial for explaining the observed
optical phenomena and the morphological properties of crystals.
The identification of minerals under the polarized-light microscope is based on optical and
morphological properties. Books that contain extensive listings of such properties provide the
data basis for the vast number of natural minerals and synthetic phases (see reference list).
This guide is based on a previously published text that has been widely used in the Germanspeaking
world, but is now out of print: “Methoden der Dünnschliffmikroskopie” by G.
Müller and M. Raith (Clausthaler Tektonische Hefte, vol.14). We adopted this text to a large
degree, revising the figures using modern graphics software, and adding many more figures
and photomicrographs to illustrate the various phenomena described in the text.
We hope that this guide will provide students with the necessary basics to master and
successfully apply polarized-light microscopy.
Suggestions are always welcome!
January 2011
Michael M. Raith, Peter Raase & Jürgen Reinhardt
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