Serpentinite
Image: James St. John (CC BY 2.0)
Mineral NameSerpentinite
Chemical Formula(Mg,Fe)₃Si₂O₅(OH)₄
Mohs Hardness2.5
Streak Colorwhite
Cleavagenone to poor (massive); perfect in one direction (fibrous varieties)
Fractureconchoidal/splintery/uneven
Specific Gravity2.65
Colorsyellowish-green, dark green, blackish-green
Transparencytranslucent/opaque
Type LocalityRed Lodge Chromite District, Rock Creek Canyon, Beartooth Mountains, Montana, USA
Mineral GroupSilicates (Phyllosilicates)
Usesdecorative stone, carving, building material, host for chromite and magnetite ores
Associated Mineralsmagnetite, chromite, talc, brucite
Raritycommon
Description
This specimen is a mottled yellowish-green rock with a rough, somewhat waxy texture, heavily speckled with numerous small, irregular black inclusions, likely magnetite.
Geological Context
This magnetitic serpentinite formed during the Precambrian through the low-temperature alteration (serpentinization) of ultramafic rocks. It is found in the Beartooth Mountains, Montana, within a district historically mined for chromium ores.
