Synthetic corundum produced by means of Verneuil method is rather easy to distinguish from natural material by the presence of curved growth lines resulting from crystallization in layers and trapped spherical gas bubbles which are never seen in natural rubies and sapphires.

PROPERTIES

General properties :

Chemistry : Al₂O₃
Crystal structure: trigonal
Purity - 99.99%

Physical properties :

Density: 3.98 (colourless) – 4.1 (dark-coloured rubies)
Hardness (Mohs scale) : 9
Tensile strength - 415 MPa
Compression strength - 180 MPa
Bending strength - 1000 MPa
Coefficient of friction with steel - 0.14
Coefficient of friction with graphite - 0.16
Coefficient of friction with graphite - 0.19

Thermal properties :

Melting point 2046°C
Limiting temperature of usage 1000 C

Optical properties :

Refraction index : 1.77