Anisotropic_Minerals - Isotropic Minerals Easily identified...

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Isotropic Minerals • Easily identified - Always extinct with upper polarizer inserted - vibration direction not changed by material - all light blocked by upper polarizer • Anisotropic usually (but not always) light with color • Measuring n important diagnostic tool - Not completely diagnostic, may vary & more than one mineral with same n - Can’t be done in thin sections • Can use other optical properties for ID, e.g. texture - color (but variable) - cleavage (may not see, control shape) - shape (depends on cut of mineral) Anisotropic Minerals • Show property called Double Refraction - light entering material usually split into two rays - depends on direction light passes through material - two rays vibrate at 90º to each other • Value of n is determined by vibration direction - one direction n larger than other. - direction with large n is slow ray - direction with small n is fast ray 1
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Optic Axis - special direction where rays not split into two rays - hexagonal and tetragonal have one optic axis - uniaxial - orthorhombic, monoclinic, and triclinic have two optic axes – biaxial Interference Phenomena • in most cases, some light passes the analyzer - specific color is interference color - caused by two rays resolving to one when they leave mineral Interference with monochromatic light • Light split into fast and slow ray - fast ray travels farther than slow ray in same time - difference in the distances called retardation, - retardation remains same after two rays leave mineral (air is isotropic) • Retardation depends on thickness (d) and the difference in n
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This note was uploaded on 07/06/2011 for the course GLY 5245 taught by Professor Staff during the Spring '11 term at University of Florida.

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Anisotropic_Minerals - Isotropic Minerals Easily identified...

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