orthoclase
A form of the mineral potassium feldspar; usually pink and a primary constituent of granite.
Portions of the summary below have been contributed by Wikipedia.
| Orthoclase | |
|---|---|
| Optical properties | |
| Crystal System: | Monoclinic |
| Color in PPL: | Colorless, commonly with a dusty or cloudy appearance |
| Pleochroism: | N/A |
| Habit/Shape: | Can be anhedral or euhedral. |
| Relief: | Low negative relief |
| Cleavage/Fracture Habit: | Has perfect cleavage on {001} and good cleavage on {010}. |
| Birefringence: | Up to first order white (roughly 0.007) |
| Extinction Habit/Angle: | Parallel extinction to cleavage |
| Length Slow/Fast: | N/A |
| Optic Sign: | Biaxial negative |
| 2Vx: | 40-70° |
| Alteration: | Commonly alters to sericite or clay. |
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