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Corundum (Al₂O₃)

corundum (D5_1) · R-3c (167)

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About

Oxygen in approximately hexagonal close packing with aluminium filling two thirds of the octahedral holes. A very hard, dense oxide — the structure of sapphire and ruby (Cr-doped corundum).

Structure

Prototypecorundum (D5_1)
Crystal systemhexagonal
Space groupR-3c (167)
Latticea = 4.7607, b = 4.7607, c = 12.9947 Å
Anglesα 90° · β 90° · γ 120°

Also crystallizes this way

α-Fe2O3 (hematite)Cr2O3Ti2O3V2O3