Material name Ruby
Composition α-Al2O3 (trace Cr ion)
Chemical formula weight 101.96
System Trigonal
Temperature (ºC) r.t.
a (Å), b (Å), c (Å) 4.759(1) 4.759(1) 12.991(5) @
α (deg), β (deg), γ (deg) 90 90 120 @
Unit cell volume (Å3) 254.8
Calculated density (g/p3) 3.99
Z 6
Space group R3c (No.167)
atom site g x/a y/b z/c B2)
Al 12c 1 0 0 0.3520(3)  -
O 18e 1 0.306(4) 0 1/4  -

Reference: R.E. Newnham and Y.M. de Haan, Zeitschrift für Kristallographie, 117, 235 (1962).