Synthetic Sapphire is a single crystal form of corundum, Al2O3, also known as alpha-alumina, alumina, and single crystal Al2O3.
Sapphire is aluminium oxide in the purest form with no porosity or grain boundaries, making it (theoretically) dense. The combination of favourable chemical, electrical, mechanical, optical, surface, thermal, and durability properties make sapphire a preferred material for high performance system and component designs. For various semiconductor applications, sapphire is the best choice in comparison with other synthetic single-crystals.
The synthetic sapphire used by diamondANVILS.com is grade 1, which means it is free of insertions, block boundaries, twins, microbubbles and scattering centers.