Potassium aluminum sulfate hydroxide formed by sulfuric acid alteration of feldspars. Indicator of epithermal ore systems. Color: White, yellowish, reddish. Luster: Vitreous to pearly. Streak: White. Cleavage: Good basal. Hardness: 3.5-4. Transparency: Translucent to opaque. Crystal system: Hexagonal Trigonal. Chemical formula: KAl₃ SO₄ ₂ OH ₆. Specific gravity: 2.6-2.9. Formation: Forms from sulfuric acid alteration of potassium-bearing rocks, typically in volcanic and hot spring environments. Common geological settings: Italy, USA, Australia, Iran; found in advanced argillic alteration zones. Common look-alikes and related entries: Kaolinite, Calcite, Dolomite.
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
2026-03-30T14:37:04.380477+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.
Potassium aluminum sulfate hydroxide formed by sulfuric acid alteration of feldspars. Indicator of epithermal ore systems.
How can you identify Alunite?
Compare several properties rather than relying on colour alone. This entry records colour: White, yellowish, reddish; lustre: Vitreous to pearly; streak: White; Mohs hardness: 3.5-4; cleavage: Good basal; crystal system: Hexagonal Trigonal; transparency: Translucent to opaque. Confirm an important identification with additional field tests or qualified laboratory work.
How does Alunite form?
Forms from sulfuric acid alteration of potassium-bearing rocks, typically in volcanic and hot spring environments.
Where is Alunite commonly found?
Italy, USA, Australia, Iran; found in advanced argillic alteration zones.
What is Alunite commonly confused with?
Alunite may be confused with Kaolinite, Calcite, Dolomite. Compare multiple diagnostic properties because colour and surface appearance can overlap.
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