Ruby is the red gem variety of the mineral corundum. Varieties of corundum are called sapphires if they are any color other than red. Chemically, a ruby is an aluminum oxide.
Rubies get their color from traces of chromium in the aluminum oxide. The red of most rubies has a brownish or yellowish tint. The rarest, most highly prized rubies are pure red.
Rubies and sapphires are second only to diamonds in hardness, and fine-quality rubies are among the costliest of all gems. The finest rubies come from Myanmar. Other primary producers of rubies are Kenya, Tanzania, and Madagascar.
A star ruby cabochon shows a six-rayed star within it when seen in a bright light. A cabochon is a rounded, polished stone.
Millions of carats of inexpensive synthetic rubies are made each year. But a demand for real gems has allowed the natural stones to maintain their high value. It can be hard to distinguish between natural and synthetic rubies, even for experts. Experts are also challenged when determining whether the color of a natural ruby has been improved by heating. Ruby is the birthstone for July.
