Gahnite
ZnAl2O4IMA symbol: Ghngrandfathered
Gahnite is an oxide or hydroxide mineral with the formula ZnAl2O4, crystallizing in the cubic system. It has a Mohs hardness of 7.5-8, typically black, brown, gray or green in color, with a greasy or vitreous luster, a specific gravity of 4. Its streak is gray.
Photos
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Crystallography
| Crystal system | cubic crystal systemWikidata (CC0) |
|---|---|
| Space group | F d -3 m :2 |
| Cell (Å, °) | a = 8.1123, b = 8.1123, c = 8.1123; α = 90, β = 90, γ = 90 |
| Cell volume | 533.866 ų, Z = 8 |
| Axial ratios | 1.0000:1:1.0000calculated from COD 9017028 |
| Source structure | COD 9017028 (American Mineralogist, 2014) — 1 of 93 structures |
Powder X-ray diffraction (calculated)
| d (Å) | 2.446 | 2.868 | 1.434 | 1.561 | 1.656 | 2.028 |
|---|---|---|---|---|---|---|
| I/I₀ | 100 | 60.1 | 54.7 | 44.5 | 19.1 | 14.2 |
xrd-v1: CuKa1 1.5406A, 2theta 5-90, top10, Imax=100, no DW/PO. Computed from COD 9017028; idealized occupancies, no preferred orientation.
Physical properties
| Density (calculated) | 4.19 g/cm³calculated from COD 9017028 |
|---|---|
| Hardness (Mohs) | 7.5-8single sourceDana, System of Mineralogy, 6th ed. (1892) |
| Specific gravity | 4 g/cm3corroboratedDana, System of Mineralogy, 6th ed. (1892) |
| Color | black, brown, gray, green, yellowsingle sourceDana, System of Mineralogy, 6th ed. (1892) |
| Streak | greysingle sourceWikidata (CC0) graysingle sourceDana, System of Mineralogy, 6th ed. (1892) |
| Luster | greasy, vitreoussingle sourceDana, System of Mineralogy, 6th ed. (1892) |
Chemistry (calculated)
| Molecular weight | 183.37 g/molcalculated from the IMA formula |
|---|---|
| Composition (wt%) | Zn 35.67%, Al 29.43%, O 34.9% |
Classification
| Nickel-Strunz (10th) | 4.BB.05Wikidata (CC0) |
|---|---|
| Nickel-Strunz (9th) | 4.BB.05Wikidata (CC0) |
| Dana (8th) | 7.2.1.4Wikidata (CC0) |