Color_elongation - Mineral Color and Pleochroism Color:...

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Mineral Color and Pleochroism Color: “True color”, not interference color - observed in plane polarized light - not crossed nicols • Many minerals are colorless • Pleochroism: property of having two true colors - occurs in anisotropic minerals - each vibration direction a unique color • color displayed when vibration direction parallel polarized direction - slow ray has one color - fast ray another color - when neither parallel to polarized direction, the color is intermediate Uniaxial Pleochroism • Description is “pleochroic formula” - one formula is color of ε and ϖ rays - alternate formula is description of greater absorbance, e.g. ε > ϖ - also describe “strong” or “weak” • Determination of formula: - find grain with δ = 0, this provides value of ϖ - find grain with maximum δ , this provides ϖ and ε - already know ϖ , so other color is ε 1
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Biaxial Pleochroism • These minerals may have three colors, one each for α , β , and γ • Procedure similar to uniaxial (slightly more complex)
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Color_elongation - Mineral Color and Pleochroism Color:...

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