Mineral Factbook

Corundum

Al2O3IMA symbol: Crngrandfathered

Corundum is an oxide or hydroxide mineral with the formula Al2O3, crystallizing in the trigonal system. It has a Mohs hardness of 9, a calculated density of 3.983 g/cm3. Its streak is white.

Photos

Corundum specimen photo
Auckland Museum Collections from Auckland, Aotearoa New Zealand · CC BY 2.0 · Commons
Corundum specimen photo
Auckland Museum Collections from Auckland, Aotearoa New Zealand · CC BY 2.0 · Commons
Corundum specimen photo
Ma, C.; Cámara, F.; Bindi, L.; Griffin, W.L. · CC BY 4.0 · Commons
Corundum specimen photo
The British Library · No restrictions · Commons

Crystallography

Crystal systemtrigonal crystal systemWikidata (CC0)
Space groupR -3 c :H
Cell (Å, °)a = 4.7605, b = 4.7605, c = 12.9956; α = 90, β = 90, γ = 120
Cell volume255.1 ų, Z = 6
Axial ratios1.0000:1:2.7299calculated from COD 1000032
Source structureCOD 1000032 (Journal of Applied Crystallography, 1990) — 1 of 27 structures

Powder X-ray diffraction (calculated)

2θ (degrees, Cu Kα1)I/I₀ (max 100)
d (Å)1.6022.0862.5521.3743.4811.741
I/I₀10098.694.26359.249.1

xrd-v1: CuKa1 1.5406A, 2theta 5-90, top10, Imax=100, no DW/PO. Computed from COD 1000032; idealized occupancies, no preferred orientation.

Physical properties

Density (calculated)3.983 g/cm³calculated from COD 1000032
Hardness (Mohs)
9single sourceWikidata (CC0)
Streak
whitesingle sourceWikidata (CC0)

Chemistry (calculated)

Molecular weight101.96 g/molcalculated from the IMA formula
Composition (wt%)Al 52.93%, O 47.07%

Classification

Nickel-Strunz (10th)4.CB.05Wikidata (CC0)
Nickel-Strunz (9th)4.CB.05Wikidata (CC0)
Dana (8th)4.3.1.1Wikidata (CC0)