Optical Techniques

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Optical Techniques

• Uniaxial Minerals

Quartz
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Uniaxial Minerals

• Anisotropic Mineral
• A crystal having only one optic axis
• Hexagonal or tetragonal crystal system
• Examples
• Quartz, calcite

nepheline
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Definitions

• Isogyres
• Areas of extinction
• Appears as a black cross (although only one arm
  may be visible at a time)
• Isochromes
• Curved interference colors
• Melatope
• Intersection of isogyres

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Isogyres, Isochromes, Melatopes
Isogyre
Melatope
Isochrome
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Determining Optic Sign

• Focus on the mineral under a low power objective
• Refocus using a higher powered objective
• Insert the accessory plate

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Sign

• Uniaxial Negative
• Blue NW, SE quadrants
• Uniaxial Positive
• Blue SW, NE quadrants