July's birthstone, the ruby, is among the most highly prized of gemstones. Large rubies are harder to find than large diamonds, emeralds and sapphires. As a result, rubies’ value increases with size more than any other gemstone.
Ruby is a pink to blood-red colored gemstone, a variety of the mineral corundum, also known as aluminum oxide. The red color is caused mainly by the presence of the element chromium. It is harder than any natural gemstone except diamond, which means a ruby is durable enough for everyday wear.
Prices of rubies are primarily determined by color. The brightest and most valuable "red" called pigeon blood-red, commands a large premium over other rubies of similar quality. After color follows clarity: similar to diamonds, a clear stone will command a premium price. Cut and carat weight would be the last determining factors in pricing a ruby.
All natural rubies have imperfections in them, including color impurities and inclusions of rutile needles known as "silk". Gemologists use these needle inclusions found in natural rubies to distinguish them from synthetics, or substitutes. Almost all rubies today are treated in some form, with heat treatment being the most common practice. Rubies that are completely untreated and are of excellent quality, command a large premium.
Rubies come from all over the world but good gemstones are found in India, Madagascar, Zimbabwe, North Carolina in the U.S., Afghanistan, Pakistan, Sri Lanka, Kenya, Tanzania, Kampuchea, and perhaps most notably, Burma. The Mogok valley of Upper Burma is famous as the source for the finest and rarest rubies of all, the pigeon blood-red, named for the stones’ intense red color. Another major source of rubies is Thailand, well-known for dark, brownish-red rubies. Both Thailand and Burma regard the ruby as their national stone.
(Information shared from the websites: American Gem Society and Earth Sky.)
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