Orthoclase
Image: <a href="//commons.wikimedia.org/wiki/User:Archaeodontosaurus" title="User:Archaeodontosaurus">Didier Descouens</a> (CC BY-SA 4.0)
Mineral NameOrthoclase
Chemical FormulaKAlSi3O8
Mohs Hardness6
Crystal Systemmonoclinic
Lustervitreous
Streak Colorwhite
CleavagePerfect in two directions at 90 degrees
Fractureuneven
Specific Gravity2.56
Colorspink, flesh-red, white, gray, yellow
Transparencytranslucent
Type LocalityMinas Gerais, Southeast Region, Brazil
Mineral GroupSilicates
Usesceramics, glass manufacturing, abrasives, gemstone (moonstone variety), collector
Associated Mineralsquartz, mica, plagioclase, hornblende
Raritycommon
Description
This large specimen of orthoclase displays prominent, blocky crystal forms with distinct cleavage planes, exhibiting a warm pinkish-brown to flesh-red color. Its surfaces show a somewhat dull to vitreous luster, characteristic of the mineral.
Geological Context
Orthoclase is a common tectosilicate mineral found in a wide range of igneous rocks, particularly felsic intrusive rocks like granite and syenite, and their extrusive equivalents. It also occurs in some metamorphic rocks, forming under various geological conditions.
