mineral
Sillimanite
Al2O3(SiO2)
AI-generated identification · may be incorrectHardness: 6.5-7.5 on the Mohs scale, Color: Brown, grayish-white, pale green, or yellow, Luster: Vitreous to silky, Crystal Structure: Orthorhombic, Cleavage: Perfect in one direction, Specific Gravity: 3.23-3.25
- Hardness
- 6
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Physical properties
Hardness: 6.5-7.5 on the Mohs scale, Color: Brown, grayish-white, pale green, or yellow, Luster: Vitreous to silky, Crystal Structure: Orthorhombic, Cleavage: Perfect in one direction, Specific Gravity: 3.23-3.25
Formation & geological history
Forms primarily through regional metamorphism of argillaceous rocks at high temperatures and pressures, typically in pelitic schists and gneisses.
Uses & applications
Used in the manufacture of high-temperature porcelain and ceramics, particularly in furnace linings and spark plugs, as well as occasionally cut as a gemstone.
Geological facts
Named after the American chemist Benjamin Silliman, sillimanite is one of the three polymorphs of aluminum silicate, the other two being andalusite and kyanite.
Field identification & locations
Identified by its fibrous or prismatic crystal habits and association with high-grade metamorphic rocks. Commonly found in Brandywine Springs, Delaware, as well as regions in France, India, and the United States.
More like this
Other mineral specimens
Gneiss or Schist
Gneiss or Mica Schist with Garnet
Metamorphic
Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
sedimentary
Epidote
Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)
metamorphic
Pegmatite with Tourmaline and Quartz
Igneous Pegmatite
igneous
Granite
Granite (Phaneritic intrusive igneous rock)
igneous
Septarian Pebble
Septarian nodule / Concretion
sedimentary