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302-pp8 - UNIVERSITY OF SOUTH ALABAMA GY 302...

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GY 302: Crystallography & Mineralogy GY 302: Crystallography & Mineralogy UNIVERSITY OF SOUTH ALABAMA Lecture 8: Native Elements Lecture 8: Native Elements
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Last Time 1. Mineral properties under XN (crossed Nichols/polars) 2. Mineral Classes/Properties 3. Native Elements; Chemistry & Crystallography (properties)
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B: Crossed Nichols (XN) 6) Extinction : occurs when the indicatrix aligns up with the polars and the entire crystal goes black (extinct). PPL PPL XN XN Optical Properties
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B: Crossed Nichols (XN) 7) Birefringence . This is the most important property of minerals under crossed polars. It is defined as the difference between the index of refraction of the minimum and maximum refractive indices of a mineral. For uniaxial minerals; n o – n e or n e - n o. For biaxial crystals; n a – n c or n c - n a . As far as you are concerned, you see pretty colours under XN Optical Properties
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Optical Properties
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