Welcome to Minerals In Thin Section

MINERALS IN THIN SECTION ("MINTS") is an open access website to view optical and morphological properties of minerals as applicable to transmitted-light microscopy, with emphasis on thin section petrography.

The MINTS site is interactive and allows to switch between Mineral Index, an Images Index (a gallery-style overview of photomicrograph series for any particular mineral), Mineral Data sheets with graphical presentations of optical-crystallographic relationships and n-Δn-d graphs, and the single Images.

This website will be updated and expanded over time. At this point, not all the listed minerals have photomicrographs attached yet, but we will make an effort to close those gaps. Generally, the database of photomicrographs and text for any particular mineral or mineral group will be expanded and reviewed from time to time.


The MINTS team:

Jürgen Reinhardt (University of the Western Cape, South Africa) - Conceptual design, compilation

Michael M. Raith (Universität Bonn, Germany) - Crystal drawings and n-Δn-d graphs


Sponsored by:



Initial webpage layout: Tanja Reinhardt (University of KwaZulu-Natal, South Africa)

Programming: James Scoble, Faghad Khan

Centre for Innovative, Education and Communication Technologies (CIECT), University of the Western Cape. Director: J. Stoltenkamp



Crystal drawings: Crystallographic elements are held in black, while indicatrix axes and vibration directions are in colour.

n-Δn graphs: the range of n for solid solutions are displayed by the coloured dots, while the maximum range of birefringence is shown by two vertical, dashed red lines. Symbols for uniaxial, biaxial, positive and negative are shown in the upper right corner.

The interference colour chart used in the Δn-d graphs is the one devised by Raith and Sørensen (European Journal of Mineralogy 25, p.8). Standard thin sections have a thickness (d) between 25 and 30 microns.

Mineral data are presented in condensed form and are not intended to replace the more detailed descriptions and compilations in standard works on optical mineralogy.

The text on the right is arranged in five colour-coded blocks: (1) chemical formula + optical data, (2) morphological data incl. extinction characteristics, (3) reaction features, (4) occurrence, and (5) distinctive properties.

Relief is classified based on a standard reference ("zero relief") value of 1.54 and logarithmic scales to the negative-relief and positive-relief sides of 1.54:


up to 1.50


1.50 - 1.54


1.54 - 1.58


1.58 - 1.67


1.67 - 1.85


1.85 - 2.2

very high

above 2.2


The reference value of 1.54 relates to the refractive index of natural Canada balsam, the standard mounting resin originally used for thin sections (1.5395 ± 0.0018; Schaller 1910), now replaced by appropriate epoxy resins.

Abbreviations for refractive indices and birefringence are those used by Tröger et al. (1979) and Raith, Raase & Reinhardt (2012), Guide to Thin Section Microscopy: no and ne for uniaxial minerals, nx, ny and nz for biaxial minerals; Δn for birefringence.

Alteration and decomposition: Only low-temperature breakdown processes (such as retrograde-hydrothermal reactions, or decomposition reactions in near-surface environments) are considered here. Under reaction textures higher-temperature breakdown reactions are considered that produce characteristic spatial associations. These depend obviously on the precise reaction history and may not necessarily be common features.




Igneous rocks


Metamorphic rocks


Sedimentary rocks and unconsolidated surface deposits


Hydrothermal environments


Not fitting into the previous categories, such as extraterrestrial materials or biomaterials


Main data sources, unless otherwise stated: Deer, Howie & Zussman (1997-2011), volumes 1 to 5, Nesse (2013), Phillips & Griffen (1981), Tröger et al. (1969, 1979), and Handbook of Mineralogy by Anthony et al. (current online version)



For each mineral, there is an image gallery. Each thumbnail image in the gallery refers to an image series that can be accessed. Every image page shows a photomicrograph, plus some information on the sample. There is a choice to view images taken under plane-polarized light (PPL) or with crossed polarizers (+Pol). Higher-resolution full-screen images (commonly between 1.5 and 2 MB*) can also be called up from the corresponding image page. To return from full screen to the previous screen use the "Back" button at the top left.

*For the image database, high-resolution photomicrographs have been downsized to ensure reasonable download speeds, while minimising the impact on image quality.

In order to keep the images free of any inserts, no scale bars are included. The true width of the photographed detail is provided, as well as the orientation of the lower polarizer. Users who intend to download images for teaching purposes are advised to provide a scale.

Section” refers to how the crystal is cut and hence corresponds to the thin section plane (= viewing plane). The notions “parallel to” and “orthogonal to” are to be understood as approximations. Images belonging to a separate subset of an image series are marked (A), (B), etc. on the image page.




(lower) polarizer

pol plane

plane of polarization

parallel to


sub-parallel to








with lambda plate (= 1ᵒ red plate) inserted


upper left


upper right


lower left


lower right

Mineral abbreviations according to Whitney & Evans (2010) and Warr (2021)

Note: Not every image series includes the full range of optically relevant mineral sections or positions. When looking for those, the series with the larger number of images should be accessed.



The website should be referenced as follows:

Reinhardt, J. & Raith, M.M., Minerals In Thin Section (MINTS). https://mints.uwc.ac.za/mints/home



Anthony, J.W., Bideaux, R.A., Bladh, K.W., Nichols, M.C. (eds.) Handbook of Mineralogy. Online compilation: Mineralogical Society of America, Chantilly, VA.

Deer, W.A., Howie, R.A. & Zussman, J. (1997-2011), Volumes 1 to 5; 2nd ed.; 1A – Orthosilicates, 1B – Disilicates and Ring Silicates, 2A – Single-Chain Silicates, 2B – Double-Chain Silicates, 3A – Micas (by M.E. Fleet), 3B – Layered Silicates Excluding Micas and Clay Minerals, 4A – Framework Silicates: Feldspars, 4B – Framework Silicates: Silica Minerals, Feldspathoids and the Zeolites (with W.S. Wise), 5A – Non-Silicates: Oxides, Hydroxides and Sulphides (by J.W.F. Bowles, R.A. Howie, D.J. Vaughan, J. Zussman), 5B – Non-Silicates: Sulphates, Carbonates, Phosphates, Halides (by L.L.Y. Chang, R.A. Howie, J. Zussman). Geological Society, London.

Nesse, W.D. (2013): Introduction to Optical Mineralogy (4th ed.). Oxford University Press, New York, 361 p.

Phillips, W.R. & Griffen, D.T. (1981): Optical Mineralogy. The Nonopaque Minerals. W.H. Freeman, San Francisco, 677 p.

Raith, M.M., Raase, P. & Reinhardt, J. (2012): Guide to Thin Section Petrography. 127 p. Open access e-book, downloadable from http://www.minsocam.org/msa/openaccess_publications.html or https://www.dmg-home.org/service/publikationen/downloads

Schaller, W.T. (1910): The refractive index of Canada balsam. American Journal of Science, Series 4, 29, p. 324.

Sørensen, B.E. (2013): A revised Michel-Lévy interference colour chart based on first-principles calculations. European Journal of Mineralogy 25, 5-10.

Tröger, W.E., Bambauer, H.U., Taborszky, F. & Trochim, H.D. (1979): Optical Determination of Rock-Forming Minerals. Part 1: Determinative Tables. E. Schweizerbart'sche Verlagsbuchandlung, Stuttgart, 188 p. (English edition of the 4th German edition).

Tröger, W.E., (1969): Optische Bestimmung der gesteinsbildenden Minerale. Teil 2, Textband, 2. Auflage, Hrsg. Bambauer, H.U., Taborzsky, F, & Trochim, H.D., E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, 822 p.

Warr, L.N. (2021): IMA-CNMNC approved mineral symbols. Mineralogical Magazine 85, 291-320.

Whitney, D.L. & Evans, B.W. (2010): Abbreviations for names of rock-forming minerals. American Mineralogist 95, 185-187.


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