Magnesium aluminum silicate showing strong pleochroism blue/violet/yellow . Gem variety iolite shows sapphire-like blue color. Color: Blue, violet, gray; strongly pleochroic. Luster: Vitreous. Streak: White. Cleavage: Poor. Hardness: 7-7.5. Transparency: Transparent to translucent. Crystal system: Orthorhombic. Chemical formula: Mg,Fe ₂Al₃ AlSi₅O₁₈. Specific gravity: 2.53-2.78. Formation: Forms during medium to high grade metamorphism of aluminum-rich pelitic rocks and in some granites. Common geological settings: India, Sri Lanka, Madagascar, Norway; found in gneisses and hornfels. Common look-alikes and related entries: Sapphire, Kyanite, Tanzanite.
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Next: Corundum — Aluminum oxide and second hardest natural mineral. Gem varieties are ruby red and sapphire all other colors .
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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Last updated
2026-03-30T14:37:49.065873+00:00
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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.
Compare several properties rather than relying on colour alone. This entry records colour: Blue, violet, gray; strongly pleochroic; lustre: Vitreous; streak: White; Mohs hardness: 7-7.5; cleavage: Poor; crystal system: Orthorhombic; transparency: Transparent to translucent. Confirm an important identification with additional field tests or qualified laboratory work.
How does Cordierite form?
Forms during medium to high grade metamorphism of aluminum-rich pelitic rocks and in some granites.
Where is Cordierite commonly found?
India, Sri Lanka, Madagascar, Norway; found in gneisses and hornfels.
What is Cordierite commonly confused with?
Cordierite may be confused with Sapphire, Kyanite, Tanzanite. Compare multiple diagnostic properties because colour and surface appearance can overlap.
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