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monoclinicuncommonSilicates
Staurolite
Fe2Al9(Si,Al)4O22(OH)2
A dark reddish-brown to brownish-black mineral often found as distinctive cruciform (cross-shaped) twins, as seen in the specimen. Its color is attributed to ferrous iron.
Staurolite Physical Properties
Mohs Hardness
7Crystal System
monoclinicLuster
vitreousStreak Color
whiteCleavage
poor on {010}Fracture
subconchoidal to unevenSpecific Gravity
3.74Colors
dark reddish-brown, brownish-black, yellowish-brownTransparency
translucent to opaqueType Locality
Piz Giuv, Switzerland; Fannin County, Georgia, USA; Brittany, FranceMineral Group
SilicatesUses
collector, indicator mineralAssociated Minerals
garnet, kyanite, andalusite, sillimanite, mica, quartzRarity
uncommonGeological Context
Staurolite is a metamorphic mineral typically formed during regional metamorphism of pelitic (clay-rich) rocks, indicating medium to high grades of metamorphism. It is an important index mineral for metamorphic conditions.
