Mineral phase
IMA name
Corundum
Secondary names
Ruby, Sapphire, Padparadscha
Class
non-silicate mineral
Compound type
oxide-hydroxide
Formula
$Al_2O_3$
Chemical formula
Al2O3
Elemental formula
Al2 O3
Isotope mixture type
terrestrial abundance
  Formula Name Family Number min-max Isotope mole fraction State Relevance
$Al$ Aluminium element 2 constituent element main
$O$ Oxygen element 3 constituent element main
Composition comments
Common impurities: Cr, Fe, V, Ti
Oxides
Formula $Al_{2}O_{3}$
Mass fraction (%) 100.0

Strunz

Class
oxides - hydroxides - arsenites (04)
Division
metal:oxygen = 2:3, 3:5, and similar (04.C)
Family
with medium-sized cations (04.CB)
Code
04.CB.05

Dana

Major class
oxides and hydroxides (III)
Class
simple oxides (04)
Type
with a cation charge of 3+ (A+++2O3) (04.03)
Group
Corundum-Hematite group (Rhombohedral: R-3c) (04.03.01)
Code
04.03.01.01
Phase type
crystalline
Crystal system
trigonal
Crystal class
ditrigonal-scalenohedral
Crystal class symbol
-3m (D3d)
Crystal spacegroup
R-3c
Molar mass
101.96 $g/mol$
Density
4 - 4.1 $g/cm^3$
State NTP
solid
Refringence type
uniaxial
Refringence sign
negative
Birefringence
0.008
Refraction index $n_o$ (w)
1.767 - 1.772
Refraction index $n_e$ (e)
1.759 - 1.763
Pure color
colorless
Color
colorless, blue, red, pink, yellow, gray, brown
Diaphaneity
transparent to translucent
Luster
vitreous