Faceted oval gemstones cut from synthetic corundum. Pure corundum, aluminum oxide, is colorless, but small amounts of chemical impurities create myriad hues. The red variety of gem quality corundum has a specific name: ruby. All other gem corundums are termed sapphire. Massive, non-gem corundum is used as an abrasive. Corundum is produced synthetically in the laboratory by a variety of methods. The synthetic (man-made) material has optical and other properties nearly identical to natural corundum.