Ruby
Ruby, gem-quality corundum (aluminum oxide) having a red color. (Blue and other varieties of gem-quality corundum are generally known as sapphire.) Rubies and sapphires are among the hardest known materials. A star ruby is a cut and polished ruby containing needle-shaped particles that reflect light in a starlike pattern.
Rubies are highly prized as gems, and the best natural rubies are even more costly than diamonds of equal weight and quality. Ruby is the birthstone for July and represents freedom. Small rubies are used for bearings in watches and other precision instruments. Ruby lasers are formed from rods of synthetic ruby.
The best natural rubies come from Mogok, Burma. Other important sources of natural rubies are Sri Lanka and Thailand. A process for making synthetic rubies by fusing chromium sesquioxide and alumina at high temperature was discovered by Auguste Verneuil, of France, in 1904.