Ribbe, Paul H. Formerly, Department of Geological Sciences, Virginia Polytechnic Institute, Blacksburg, Virginia.
- Additional Readings
Triclinic potassium feldspar, KAlSi3O8, that usually contains a few percent sodium feldspar (Ab = NaAlSi3O8) in solid solution. Its hardness is 6; specific gravity, 2.56; mean refractive index, 1.52; color, white (green varieties are called amazon stone or amazonite; see illustration). Good (001) and (010) planar cleavages are inclined at 90.4°. Microcline is found in some relatively high-grade regional metamorphic rocks, but is much more common in pegmatities, granites, and related plutonic igneous rocks. In the last, it often occurs as a microcline perthite, containing exsolved low albite intergrowths. See also: Perthite
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