Image: <bdi><a href="https://www.wikidata.org/wiki/Q56247090" class="extiw" title="d:Q56247090"><span title="mineral collector and dealer">Robert M. Lavinsky</span></a></bdi> (CC BY-SA 3.0)
monoclinicuncommonSilicates
Staurolite
(Fe,Mg)2Al9(Si,Al)4O22(OH)2
This specimen features a dark reddish-brown, opaque staurolite crystal, prominently displaying its characteristic 90-degree cruciform twinning, which forms a distinct cross shape. The crystal has a somewhat rough, dull to resinous luster.
Staurolite Physical Properties
Mohs Hardness
7Crystal System
monoclinicLuster
vitreousStreak Color
white to grayishCleavage
distinct on {010}, poor on {110}Fracture
subconchoidalSpecific Gravity
3.78Colors
reddish-brown, dark brown, yellowish-brown, blackish-brownTransparency
translucent to opaqueType Locality
Rubelita, Minas Gerais, Southeast Region, BrazilMineral Group
SilicatesUses
collector, jewelry, good luck charmAssociated Minerals
garnet, kyanite, sillimanite, andalusite, muscovite, biotite, quartzRarity
uncommonGeological Context
Staurolite is a nesosilicate mineral formed during regional metamorphism of argillaceous rocks, typically found in schists and gneisses. Its presence indicates medium- to high-grade metamorphic conditions, making it a valuable index mineral for geologists.
