Ruby

A ruby is a pink to blood-red colored gemstone, a variety of the mineral corundum (aluminium oxide). Other varieties of gem-quality corundum are called sapphires. Ruby is one of the traditional cardinal gems, together with amethyst, sapphire, emerald, and diamond. The word ruby comes from ruber, Latin for red. The color of a ruby is due to the element chromium.

Formation & Geology

Rubies are formed under immense heat and pressure below the earth's surface. They are found in metamorphic rocks such as marble, gneiss, and schist. The best rubies are typically found in marble deposits (such as in Myanmar), where the low iron content allows for infinite fluorescence and intense red color. Basalt-hosted rubies (like those from Thailand) have higher iron content which can dampen the color.

Physical Characteristics

The most important factor in the value of a ruby is color. The brightest and most valuable red is called pigeon blood-red, commanding a large premium over other rubies of similar quality. After color follows clarity: similar to diamonds, a clear stone will command a premium. Rubies are extremely hard, measuring 9 on the Mohs scale, second only to diamond.

Historical Significance

Historically, rubies have been revered in many cultures. In Sanskrit, ruby is 'ratnaraj', meaning 'King of Precious Stones'. Ancient Hindus believed those who offered fine rubies to the god Krishna were granted rebirth as emperors. In Biblical history, rubies are mentioned often as the most precious of gems.

Treatments & Enhancements

Almost all rubies on the market today are heat-treated to improve color and dissolve "silk" (rutile inclusions) to increase clarity. This is a stable and accepted practice. Some lower-quality rubies are "glass-filled" (fracture filled) to hide cracks; these are significantly less valuable and require special care as the filler can be damaged by household cleaners.