Sapphire has a rhombohedral type structure and is a highly anisotropic material, with properties that are largely dependent on crystallographic orientation. The properties shown in the table are average values for different orientations. More detailed property information can be obtained by e-mailing: sales@crystalsystems.com

The melting point of sapphire is 2040 °C, and it has extremely high chemical stability even at high temperatures. Sapphire's energy gap of 9.1 eV is one of the largest for oxide crystals, which permits excellent optical transmission with very little absorption from about 0.250 to 5.0 microns.

Sapphire is the material of choice for stringent optical applications involving exposure to high stresses and harsh environments. Sapphire is one of the strongest and hardest materials available; it has excellent abrasion resistance and exceptional thermal shock properties. The hardness of sapphire on the Mohs scale is 9, compared to 10 for diamond.

The strength of sapphire largely depends on the surface finish quality and subsurface damage caused by manufacturing processes. The selection of appropriate polishing techniques and heat treatments significantly improves the strength of sapphire. For design criteria, a tensile strength of 400 mpa (58,000 psi) is often chosen.