Sillimanite
Species
Common · Al₂SiO₅
One of three minerals sharing the formula Al₂SiO₅, and the one that marks the hottest metamorphism; kyanite and andalusite hold the same atoms at lower temperatures. Its fibrous masses cut fine cat's-eyes.
Identity
- Formula
- Al₂SiO₅
- Chemical class
- Silicate
- Also known as
- Fibrolite
Crystallography
- Crystal system
- Orthorhombic
- Habits
- Fibrous, Prismatic, Columnar
- Fracture
- Uneven
Physical properties
- Mohs hardness
- 7
- Density
- 3.24 g/cm³
- Luster
- Vitreous
- Colors
- blue, brownish green, colorless, gray, gray green
- Streak
- white
- Transparency
- Transparent, Translucent
Geology
- Origins
- Metamorphic
- Host rocks
- Schist and gneiss
- Associated minerals
- Kyanite, andalusite, Garnet, biotite, Quartz
- Geography
- India, Sri Lanka, USA
Classification
- Rarity
- Common
- Gem quality
- Yes
Sources
- M. Pasero and others, IMA Commission on New Minerals, Nomenclature and Classification, The New IMA List of Minerals, updated September 2026. International Mineralogical Association (CNMNC), 2026.
- Sillimanite. Mindat.org (Hudson Institute of Mineralogy).
- J. W. Anthony, R. A. Bideaux, K. W. Bladh, M. C. Nichols, Sillimanite. Mineral Data Publishing, Handbook of Mineralogy, 2001.
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