Staurolite
Image: Strekeisen (CC BY-SA 4.0)
Mineral NameStaurolite
Chemical Formula(Fe,Mg)2Al9(Si,Al)4O22(OH)2
Mohs Hardness7
Crystal Systemorthorhombic
Lustervitreous
Streak Colorwhite to grayish white
Cleavagepoor on {010}
Fracturesubconchoidal to uneven
Specific Gravity3.78
Colorsreddish-brown, dark brown, yellowish-brown, black
Transparencytranslucent to opaque
Type LocalityPosada Asinara shear zone, Sardinia (Italy)
Mineral GroupSilicates
Usesindicator mineral, collector, rarely gemstone
Associated Mineralsgarnet, kyanite, sillimanite, andalusite, muscovite, biotite, quartz
Rarityuncommon
Description
This image displays a thin section of a twinned staurolite crystal, appearing yellowish-brown with numerous internal fractures or cleavage planes, set against a lighter, fine-grained matrix. Small green inclusions are also visible within the field of view.
Geological Context
Staurolite is a metamorphic index mineral that forms during medium- to high-grade regional metamorphism of pelitic rocks, indicating specific pressure and temperature conditions. Its presence in a shear zone suggests formation under significant tectonic stress.
