mineral
Feldspar (Plagioclase / Orthoclase)
KAlSi3O8 / CaAl2Si2O8 - NaAlSi3O8
Mohs hardness 6, white to pale off-white color, vitreous to pearly luster, monoclinic or triclinic crystal structure, perfect cleavage in two directions at nearly 90 degrees, specific gravity 2.55-2.76
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Physical properties
Mohs hardness 6, white to pale off-white color, vitreous to pearly luster, monoclinic or triclinic crystal structure, perfect cleavage in two directions at nearly 90 degrees, specific gravity 2.55-2.76
Formation & geological history
Formed primarily during the crystallization of intrusive and extrusive igneous rocks (such as granite and basalt) as well as metamorphic rocks. Major rock-forming mineral family found worldwide.
Uses & applications
Used extensively in ceramic glazes, glassmaking, porcelain manufacture, mild abrasives, and as decorative stone in construction.
Geological facts
Feldspar is the single most abundant mineral group in Earth's continental crust, making up about 60% of the Earth's crust by weight.
Field identification & locations
Identified in the field by its blocky cleavage faces, porcelain-like or vitreous luster, hardness of 6 (cannot be scratched by a steel nail), and milky white to pinkish-tan coloration. Commonly found in pegmatites and granitic terrains worldwide.
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Other mineral specimens
Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
sedimentary
Schist
Schist
Metamorphic
Sandstone with Mineral Veining or Crust
Sedimentary Sandstone (mostly SiO2 with Fe2O3 tinting)
sedimentary
Potassium Feldspar (Orthoclase)
Orthoclase (KAlSi3O8)
mineral
Gypsum (variety Selenite or Alabaster)
Calcium sulfate dihydrate (CaSO4·2H2O)
Mineral
Nephrite Jade
Nephrite
Mineral/Rock