What Variety of Corundum Are Sapphires?

Corundum may appear in many colors, such as blue sapphires or red rubies.

The blue variety of corundum is referred to in the gem trade as a sapphire. However, other varieties of corundum are referred to as a colored sapphire. For example, green sapphire refers to green corundum. Scientifically, sapphire refers to all color varieties of corundum except red (ruby) and black (emery).

Corundum Properties

Corundum is a mineral composed of aluminum oxide (Al2O3). These gems have a hardness of 9 on Moh's relative scale of hardness, second only to diamonds among minerals. Corundum has a glassy appearance and can appear in a variety of colors.

Naming Convention

The term sapphire has long referred to corundum. Previously, other colors of corundum were named as an oriental version of the stone they resembled. For instance, green corundum was referred to as oriental emerald. This naming convention was eventually abandoned in favor of the current system.

Synthetic Corundum

The development of synthetic corundum by flame fusion more than a century ago had a devastating effect on ruby and sapphire mining operations as the price of the stones fell. Synthetic corundum is still made for applications in industry and for gems. Ruby and sapphire mines still operate but at a greatly reduced capacity.

References

• University of Texas at Austin: Corundum
• The Mineral and Gemstone Kingdom: Corundum
• Corundum Mineral Data