Alunite
KAl3(SO4)2(OH)6IMA symbol: Aluredefined
Alunite is a sulfate mineral with the formula KAl3(SO4)2(OH)6, crystallizing in the trigonal system. It has a Mohs hardness of 3.5-4, typically white, gray or red in color, with a pearly or vitreous luster, a specific gravity of 2.58-2.752. Its streak is white.
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Crystallography
| Crystal system | trigonal crystal systemWikidata (CC0) |
|---|---|
| Space group | R -3 m :H |
| Cell (Å, °) | a = 6.9749, b = 6.9749, c = 17.315; α = 90, β = 90, γ = 120 |
| Cell volume | 729.506 ų, Z = 3 |
| Source structure | COD 9016102 (Mineralogical Magazine, 2012) — 1 of 12 structures |
Physical properties
| Hardness (Mohs) | 3.5-4single sourceDana, System of Mineralogy, 6th ed. (1892) |
|---|---|
| Specific gravity | 2.58-2.752 g/cm3single sourceDana, System of Mineralogy, 6th ed. (1892) |
| Color | gray, red, whitesingle sourceDana, System of Mineralogy, 6th ed. (1892) |
| Streak | whitesingle sourceWikidata (CC0) whitesingle sourceDana, System of Mineralogy, 6th ed. (1892) |
| Luster | pearly, vitreoussingle sourceDana, System of Mineralogy, 6th ed. (1892) |
Chemistry (calculated)
| Molecular weight | 414.21 g/molcalculated from the IMA formula |
|---|---|
| Composition (wt%) | K 9.44%, Al 19.54%, S 15.48%, O 54.08%, H 1.46% |
Classification
| Nickel-Strunz (10th) | 7.BC.10Wikidata (CC0) |
|---|---|
| Nickel-Strunz (9th) | 7.BC.10Wikidata (CC0) |
| Dana (8th) | 30.2.4.1Wikidata (CC0) |