Sillimanite identification and geology

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Sources, scope & corrections

These authoritative resources support category-level nomenclature, terminology, identification methods, and safety. When a specimen-specific safety warning appears, the public-health source listed here directly supports that precaution. They are not line-by-line citations for every other property on this entry, and natural specimens vary.

Editorial owner

GeoMiner

Last updated

2026-03-30T14:36:54.544193+00:00

Review status

Published; not independently peer-reviewed

• IMA–CNMNC List of Mineral Names — International Mineralogical Association. Official mineral-name, nomenclature, and classification records.
• Mineral ID Key — Mineralogical Society of America. Physical-property identification methods, repeat-testing guidance, and limitations.

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Common questions

What is Sillimanite?

High-temperature aluminum silicate polymorph forming fibrous or prismatic crystals. Indicates high-grade metamorphism.

How can you identify Sillimanite?

Compare several properties rather than relying on colour alone. This entry records colour: White, gray, brown, greenish; lustre: Vitreous to silky; streak: White; Mohs hardness: 6-7; cleavage: Perfect in one direction; crystal system: Orthorhombic; transparency: Transparent to translucent. Confirm an important identification with additional field tests or qualified laboratory work.

How does Sillimanite form?

Forms during high-temperature regional metamorphism of aluminum-rich pelitic rocks.

Where is Sillimanite commonly found?

Sri Lanka, India, USA, Kenya; found in high-grade pelitic schists and gneisses.

What is Sillimanite commonly confused with?

Sillimanite may be confused with Kyanite, Andalusite, Wollastonite. Compare multiple diagnostic properties because colour and surface appearance can overlap.