A few gem materials are organic substances or have an animal or vegetable origin. The pearl, for example, is formed from secretions of molluscs. In 1902 Auguste Verneuil of Paris established the first commercially successful process for making such synthetic gems. The chief raw material is extremely pure, powdered aluminium. This is sifted through an intense oxyhydrogen flame, and the fused material drops down on a sticklike support.
Pure alumina yields white sapphire.
Mixed with a small amount of chromium oxide, it makes synthetic ruby. Other mixtures yield blue, green, rose, or violet sapphires. A variation of the Verneuil process, developed in the United States in World War II, produces slender rods up to 30 inches long. They are especially useful in the manufacture of jewelled bearings for precision instruments. Synthetic gems are used principally in industry.