guide to thin section microscopy - Mineralogical Society of America
guide to thin section microscopy - Mineralogical Society of America
guide to thin section microscopy - Mineralogical Society of America
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Guide <strong>to</strong> Thin Section Microscopy<br />
Colour and pleochroism<br />
In optically anisotropic substances (non-cubic minerals), absorption is a directional<br />
property. Thus, crystals <strong>of</strong> a single mineral species can display different colours dependent on<br />
their orientation and corresponding light vibration directions. Colours and pleochroism are<br />
mineral-specific properties.<br />
The majority <strong>of</strong> minerals do not show any, or only weak, pleochroism. Exceptions displaying<br />
strong pleochroism are <strong>to</strong>urmaline, members <strong>of</strong> the amphibole group, Fe-Ti-rich biotites, and<br />
less common minerals such as piemontite, sapphirine, dumortierite and yoderite. Fig. 4-10<br />
shows examples <strong>of</strong> distinct <strong>to</strong> strong pleochroism.<br />
Raith, Raase & Reinhardt – February 2012<br />
Figure 4-10. Examples <strong>of</strong> distinct <strong>to</strong> strong pleochroism.<br />
A: Piemontite. B: Glaucophane. C: Sapphirine. D: Viridine. E: Thulite. F: Yoderite (by courtesy <strong>of</strong> Dr. N. Jöns,<br />
Universität Bremen). G: Chlori<strong>to</strong>id. H: Biotite. I: Ti-rich biotite. J: Lazulite. K: Aegirine augite. L: Fe 3+ -rich<br />
epidote (pistacite).<br />
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