Aluminum oxide and second hardest natural mineral. Gem varieties are ruby red and sapphire all other colors . Color: Variable: red ruby , blue, yellow, pink sapphire. Luster: Adamantine to vitreous. Streak: White. Cleavage: None parting common. Hardness: 9. Transparency: Transparent to opaque. Crystal system: Hexagonal Trigonal. Chemical formula: Al₂O₃. Specific gravity: 3.98-4.10. Formation: Forms in aluminum-rich, silica-poor metamorphic rocks and in some igneous rocks like syenites. Common geological settings: Myanmar, Sri Lanka, Kashmir, Madagascar, Montana; found in marbles, gneisses, and alluvial deposits. Common look-alikes and related entries: Spinel, Garnet, Topaz.
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.
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GeoMiner
Last updated
2026-03-30T14:36:56.295655+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.
Aluminum oxide and second hardest natural mineral. Gem varieties are ruby red and sapphire all other colors .
How can you identify Corundum?
Compare several properties rather than relying on colour alone. This entry records colour: Variable: red ruby , blue, yellow, pink sapphire; lustre: Adamantine to vitreous; streak: White; Mohs hardness: 9; cleavage: None parting common; crystal system: Hexagonal Trigonal; transparency: Transparent to opaque. Confirm an important identification with additional field tests or qualified laboratory work.
How does Corundum form?
Forms in aluminum-rich, silica-poor metamorphic rocks and in some igneous rocks like syenites.
Where is Corundum commonly found?
Myanmar, Sri Lanka, Kashmir, Madagascar, Montana; found in marbles, gneisses, and alluvial deposits.
What is Corundum commonly confused with?
Corundum may be confused with Spinel, Garnet, Topaz. Compare multiple diagnostic properties because colour and surface appearance can overlap.
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