Solid phase
Official name
alpha-Aluminium(III) oxide
Secondary names
Aluminium oxide; Aluminum oxide; Synthetic Corundum; Alumina; alpha-Al2O3
CAS number
1344-28-1
Type
Family
ionic solid
Class
tridimentional covalent network solid
Compound type
oxide
Comments
Aluminium oxide also exist in a number of other crystalline phases
Chemical composition
Formula
$Al^{3+}_2O^{2-}_3$
Chemical formula
Al2O3
Elemental formula
(Al3+)2 (O2-)3
Isotope mixture type
terrestrial abundance
10.0
  Formula Name Family Number min-max Mole fraction Isotope mole fraction State Relevance
$Al^{3+}$ Aluminium(III) cation element 2 0.4 1 constituent cation main
$O^{2-}$ Oxide anion element 3 0.6 1 constituent anion main
Composition comments
partly ionic and covalent bond network
Chemical bonds
  Bond Number
$\cdot (\cdot) Al^{3+} \cdot O^{2-} \cdot$ 6
Class
tridimensional covalent networks (11)
Type
metal homonuclear tridimensional networks (elemental) (11.02)
Equivalent mineral
Corundum
Phase name
$\alpha\-Al_2O_3$
Phase type
crystalline
Crystal system
trigonal
Crystal class
ditrigonal-scalenohedral
Crystal class symbol
-3m (D3d)
Crystal spacegroup
R-3c
Composition order
ordered
Molar mass
101.96 $g/mol$
Density
3.987 $g/cm^3$
State NTP
solid
Phase transitions
Phase transition type Other phases Temperature - Pressure
solid-liquid liquid Al2O3 2072 °C (2345 K)
Refringence type
uniaxial
Refringence sign
negative
Birefringence
0.008
Refraction index $n_{\alpha}$
1.768 - 1.772
Refraction index $n_{\beta}$
1.760 - 1.763
Pure color
colorless
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