Anorthosite
Image: James St. John (CC BY 2.0)
Mineral NameAnorthosite
Chemical Formula(Na,Ca)(Al,Si)AlSi2O8
Mohs Hardness6
Crystal Systemtriclinic
Streak Colorwhite
CleavageTwo good cleavages at nearly 90 degrees
Fractureuneven to conchoidal
Specific Gravity2.62
Colorsgray, white, bluish-gray
Transparencyopaque
Type LocalitySplit Rock Lighthouse, Minnesota, USA
Mineral GroupSilicates
Usesbuilding stone, dimension stone, aggregate
Associated Mineralspyroxene
Raritycommon
Description
The image displays a large, weathered outcrop of anorthosite, characterized by its grayish color, rough texture, and visible subtle layering, with some lichen growth.
Geological Context
Anorthosite is a coarsely-crystalline intrusive igneous rock predominantly composed of plagioclase feldspar, forming this Precambrian layered inclusion within the Mesoproterozoic Beaver River Diabase.
