Gibbsite
Al(OH)3IMA symbol: Gbsapproved
Gibbsite is an oxide or hydroxide mineral with the formula Al(OH)3, crystallizing in the monoclinic system. It has a Mohs hardness of 2.5-3.5, typically white, gray, green or red in color, with a pearly or vitreous luster, a specific gravity of 2.3-2.4. Cleavage is eminent.
Photos
Crystallography
| Crystal system | monoclinic crystal systemWikidata (CC0) |
|---|---|
| Space group | P 1 21/n 1 |
| Cell (Å, °) | a = 8.675, b = 5.069, c = 9.726; α = 90, β = 94.55, γ = 90 |
| Cell volume | 426.34 ų, Z = 8 |
| Axial ratios | 1.7114:1:1.9187calculated from COD 1544375 |
| Source structure | COD 1544375 (Z. Kristallogr., 2007) — 1 of 6 structures |
Powder X-ray diffraction (calculated)
| d (Å) | 4.848 | 4.373 | 2.386 | 4.324 | 2.05 | 1.805 |
|---|---|---|---|---|---|---|
| I/I₀ | 100 | 37.1 | 20.9 | 17.7 | 16.8 | 15.1 |
xrd-v1: CuKa1 1.5406A, 2theta 5-90, top10, Imax=100, no DW/PO. Computed from COD 1544375; idealized occupancies, no preferred orientation.
Physical properties
| Density (calculated) | 2.431 g/cm³calculated from COD 1544375 |
|---|---|
| Hardness (Mohs) | 2.5-3.5single sourceDana, System of Mineralogy, 6th ed. (1892) |
| Specific gravity | 2.3-2.4 g/cm3corroboratedDana, System of Mineralogy, 6th ed. (1892) |
| Color | gray, green, red, white, yellowsingle sourceDana, System of Mineralogy, 6th ed. (1892) |
| Luster | pearly, vitreoussingle sourceDana, System of Mineralogy, 6th ed. (1892) |
| Cleavage | eminentDana, System of Mineralogy, 6th ed. (1892) |
Chemistry (calculated)
| Molecular weight | 78.0 g/molcalculated from the IMA formula |
|---|---|
| Composition (wt%) | Al 34.59%, O 61.53%, H 3.88% |
Classification
| Nickel-Strunz (10th) | 4.FE.10Wikidata (CC0) |
|---|---|
| Nickel-Strunz (9th) | 4.FE.10Wikidata (CC0) |