FACTS ABOUT RUBY - The July Birth Stone
Ruby, the July birth stone, is a precious gem that occurs as a red, transparent variety of the mineral corundum, which is the second hardest mineral after diamond. Sapphire includes all other colored gem variety.
Ruby color varies in different specimens from rose red through so-called ruby red and carmine to a deep purplish red, called "pigeon blood." Clear stones of the deeper shades are the most highly prized.
Many stones that are not rubies are nevertheless called rubies. The balas, or balas ruby, for example, is a type of spinel; the Bohemian ruby is rose quartz; the Siberian ruby is red or pink tourmaline; American ruby, Cape ruby, Montana ruby, and Rocky Mountain ruby are varieties of garnet.The finest rubies are found in central Myanmar (formerly known as Burma) in the neighborhood of Mogok, where rubies have been found since the 15th century in metamorphosed limestones as well as in the overlying weathered zones. Important deposits of rubies are also found in Thailand, Afghanistan, Sri Lanka, India, China, and the former Soviet republics.
Precious Corundums are sought after; especially fine rubies are much appreciated and can achieve prices surpassed only by emeralds and diamonds.
In the U.S. rubies are mined in North Carolina and near Helena, Montana.
In addition to their importance as highly prized gems, these July birth stones are used in industry as jeweled bearings in watches and scientific instruments.
Synthetic rubies were first produced in 1837 by fusing alum and chromium-oxide pigment at a high temperature. Improvements in the manufacture of synthetic rubies since then have made possible the production of synthetic stones, which are very much like the natural stone in physical and chemical properties. Synthetic rubies are used as gems, but about 75 percent of the annual production of synthetic rubies are used in the manufacture of watches and instruments.
Other famous rubies are the 167 carat Edwards ruby (British Museum) and 100 carat DeLong star ruby.
The Black Prince Ruby in the Imperial State Crown in London is actually a 170 carat spinel.
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When cut into a cabochon (a nonconvex) form, some specimens of ruby exhibit asterism; that is, a six-rayed star can be seen in the interior of the stone caused by inclusions, which are needle-like extensions of other mineral crystals (such as rutile) trapped within the primary stone. Such rubies, called star rubies, are also highly prized.
The Rosser Reeves stone (left) is one of the finest star rubies. It weighs 138.7 carats.