Corundum ruby

Category: Oxide mineral – Hematite group

Chemical formula: Aluminium oxide, Al2O3

Strunz classification: 04.CB.05

Dana classification: 4.3.1.1

Crystal symmetry: Trigonal (32/m)

Unit cell: a = 4.75 Å, c = 12.982 Å; Z=6

Crystal system: Trigonal (Hexagonal Scalenohedral) Symbol (32/m) Space group: R3c

Mohs scale hardness; 9 (defining mineral)

Specific gravity: 3.95–4.10

Optical properties: Uniaxial (–)

Refractive index: nω = 1.767–1.772 nε = 1.759–1.763

Pleochroism: None

Melting point: 2044 °C


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