Serpentinite
Image: James St. John (CC BY 2.0)
Mineral NameSerpentinite
Chemical Formula(Mg,Fe)₃Si₂O₅(OH)₄
Mohs Hardness2.5
Crystal Systemmonoclinic
Streak Colorwhite
Cleavagegood in one direction (for constituent minerals), often not apparent in massive rock
Fracturesplintery
Specific Gravity2.6
Colorsgreen, yellowish-green, black
Transparencytranslucent
Type LocalityRed Lodge Chromite District, Rock Creek Canyon, Beartooth Mountains, Montana, USA
Mineral GroupSilicates
Usesdecorative stone, carving, industrial filler, building material
Associated Mineralsmagnetite, chromite, talc, magnesite, olivine, pyroxene
Raritycommon
Description
This specimen is a yellowish-green rock with a somewhat greasy luster, appearing wet, and is speckled with numerous small, dark black inclusions.
Geological Context
Serpentinite is a metamorphic rock formed by the hydrothermal alteration (serpentinization) of ultramafic rocks like peridotite or dunite, rich in olivine and pyroxene. This Precambrian specimen from Montana is associated with chromium ores, indicating a geological setting often linked to ophiolites or layered intrusions.
