Minerals In Thin Section

Explanations

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	moderate-negative
1.50 - 1.54	low-negative
1.54 - 1.58	low-positive
1.58 - 1.67	moderate-positive
1.67 - 1.85	high
1.85 - 2.2	very high
above 2.2	extreme

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: n_o and n_e for uniaxial minerals, n_x, n_y and n_z 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.

Occurrence

Ign	Igneous rocks
Met	Metamorphic rocks
Sed	Sedimentary rocks and unconsolidated surface deposits
Hydr	Hydrothermal environments
Other	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)

Images

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.

Abbreviations

pol	(lower) polarizer
pol plane	plane of polarization
∥	parallel to
sub-∥	sub-parallel to
ext	extinction
mag	magnification
Δn	birefringence
+1λ	with lambda plate (= 1ᵒ red plate) inserted
u.l.	upper left
u.r.	upper right
l.l.	lower left
l.r.	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.

Referencing

The website should be referenced as follows:

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

Literature

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 (4^th 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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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.