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)
orthorhombiccommonSilicates
Sillimanite
Al₂SiO₅
The image displays a fibrous aggregate of sillimanite, exhibiting a grayish-white color and a somewhat silky luster, characteristic of its common habit.
Sillimanite Physical Properties
Mohs Hardness
6.5Crystal System
orthorhombicLuster
vitreousStreak Color
whiteCleavage
perfect on {010}Fracture
unevenSpecific Gravity
3.25Colors
white, gray, brown, pale green, pale blueTransparency
transparentType Locality
Yantic Falls, Norwich, New London County, Connecticut, USAMineral Group
SilicatesUses
refractory material, industrial ceramics, gemstone (rarely)Associated Minerals
kyanite, andalusite, garnet, cordierite, biotite, muscovite, quartz, feldsparRarity
commonGeological Context
Sillimanite is a high-temperature, moderate-to-high pressure metamorphic mineral, typically found in pelitic (aluminum-rich) rocks during regional metamorphism. It serves as an index mineral, indicating high-grade metamorphic conditions.
