Sanidine
Image: <a href="//commons.wikimedia.org/wiki/User:Archaeodontosaurus" title="User:Archaeodontosaurus">Didier Descouens</a> (CC BY-SA 4.0)
Mineral NameSanidine
Chemical FormulaKAlSi3O8
Mohs Hardness6
Crystal Systemmonoclinic
Lustervitreous
Streak Colorwhite
CleavagePerfect on {001}, good on {010}, parting on {110}
Fractureuneven
Specific Gravity2.56
Colorslight brown, gray, white, colorless
Transparencytranslucent
Type LocalityPuy de Sancy, Monts-Dore massif, Puy-de-Dôme, Auvergne, France
Mineral GroupSilicates (Feldspar Group)
Usescollector, geological indicator
Associated Mineralsquartz, biotite, hornblende, plagioclase
Raritycommon
Description
This image displays a large, blocky, light brownish-gray sanidine crystal exhibiting characteristic Carlsbad twinning, giving it a somewhat angular and stepped appearance.
Geological Context
Sanidine is a high-temperature potassium feldspar that forms in rapidly cooled volcanic rocks such as rhyolites and trachytes, often as phenocrysts in extrusive igneous environments.
