Ruby is red corundum, all other color varieties of corundum being referred to as sapphire. Corundum is the second hardest substance on the Mohs Scale, with a rating of 9. Diamond tops the scale with a rating of 10. Excellent hardness combined with the rich color and silky shine makes fine ruby so valuable and secures them a position as one of the so-called "precious" gemstones.Ruby is named after the Latin word "ruber" for red. Ruby is one of the most expensive gems, large rubies being rarer than comparable diamonds. Many rubies are an essential part of royal insignia and other famous jewelry.Ruby is the birthstone for those who are born in July. Ruby is also used to celebrate a couple's 15th and 40th anniversary.
Rubies range in color from pinkish to orangey and purplish and brownish red, depending on the chromium and iron content of the stone. The most desirable color is the so-called "pigeon's blood", a pure red with a hint of blue.
Color is the most important consideration, with clarity a distant second. Large rubies are rare.
The most desirable color is the so-called "pigeon's blood", a pure red with a hint of blue. Color saturation makes all the difference.
Ruby shows pleochroism which means that the color varies with the direction of viewing. Stones displaying the cat's eye or star effect are best viewed in daylight.Many rubies will fluoresce in long or short wave UV and this property can often be used to help identify a stone's geographic origin. Burmese rubies often fluoresce so strongly that the effect is noticeable even in sunlight; such stones seem literally to glow. Thai rubies generally lack this property.
Inclusions are common in ruby and not always an indication of lower quality. Included rutile needles cause the "silky shine". If such a stone is cut en cabochon it exposes the rare cat's eye effect. Oriented rutile crystal inclusions cause a six-rayed-star light effect (called asterism) to form the popular star ruby.
Transparent rubies are cut in step and brilliant cut. Less transparent rubies are cut en cabochon.
Ruby location and deposits
Myanmar: For centuries the most important deposits are in upper Myanmar (Burma) near Mogok. Only one percent of the production is of gem quality. Some of the rubies are of pigeon's blood color and considered to be the most valuable rubies of all. In the early 1990's large new deposits were discovered at Mong Hsu.