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 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.
Thailand: Rubies found in Thailand (Chanthaburi district) often have a brown or violet tint. The Thai ruby production is declining, and Chanthaburi is now mainly a center for processing and trading gems.
Sri Lanka: The deposits are located in the southwest of the island in the Ratnapura district. Rubies from that deposits are usually light red to raspberry red.
Madagascar: in the 1990’s major ruby deposits were discovered in this huge island off the coast of Mozambique. Madagascar is now one of the world’s leading ruby producers.
Tanzania: On the upper Umba River in northwest Tanzania are deposits for gemstone quality rubies that are violet to brown-red. A few opaque rubies are mined as well.
Other deposits of some importance are found in: Afghanistan, Cambodia, Kenya and Vietnam. Less significant deposits are in: Australia, Brazil, India, Malawi, Nepal, Pakistan, United States and Zimbabwe.
Common Ruby treatments
The most common treatment for ruby is heat treatment. Stones, generally before they are cut, are heated to between 1700 to 1800 degrees Celsius (3100-3300 degrees F) for several hours. Heating often improves both color and clarity. A reputable dealer will always disclose gem treatments.
Lower grade rubies with surface-reaching fissures are often fracture-filled with lead glass. This treatment produces good looking stones that can be sold at a very reasonable price.
Famous stones of outstanding beauty and color are the “Edwardes Ruby”,weight 167 ct, displayed at the British Museum of Natural History in London, the “Rosser Reeves Star Ruby”, of 138.7 ct, to be seen at the Smithsonian Institution in Washington, the “De Long Star Ruby”, weight 100 ct, shown in the American Museum of Natural History in New York and the “Peace Ruby”, 43 ct, which was found in 1919.
Many rubies are an essential part of royal insignia and other famous jewelry. The Bohemian St. Wenzel’s Crown holds an unfaceted ruby of about 250 ct.
Some famous large rubies, such as the “Black Prince’s Ruby” and the “Timur Ruby” in the British Crown Jewels are actually spinels, because until the beginning of the 19th century spinels were thought to be rubies.
Rubies are one of the favorite gems of the rich and famous. Elizabeth Taylor owns a spectacular ruby necklace and earring set. During an auction of the estate of Jacqueline Kennedy Onassis by Sotheby’s on April 24, 1996, a 17.68-carat ruby ring sold for $290,000; some cabochon ruby earrings sold for $360,000; and a cabochon ruby necklace was a bargain at $247,500. Marlene Dietrich owned a ruby bracelet that sold at Sotheby’s for $990,000.
Rubies have also a famous place in science – the first lasers were made from artificial ruby crystals.
Color: Varying red
Chemical composition: Al2O3 aluminum oxide
Crystal system: (Trigonal) hexagonal prisms or tables, rhombohedrons
Hardness: 9 (Mohs scale)
Specific gravity: 3.97 – 4.05
Refractive index: 1.762 -1.778
Color of streak: White,
Absorption spectrum: 694, 693, 668, 659, 610-500, 476, 475, 468
Fluorescence: Strong carmine red
The Ruby zodiac, myth & legend
For a long time India was considered as the classical source of rubies. In the Sanskrit language ruby is called “ratnaraj”, which translates as “King of Gemstones”.
In ancient times one of the chief attractions of ruby has been its protection from misfortune and bad health.
Ruby is the birthstone for those who are born in July. On the Zodiac chart, ruby is the stone for Capricorn.
Ruby is also used to celebrate a couple’s 15th and 40th anniversary.
In Antiquity, as well as in the Middle Ages people believed that the cosmos is reflected in gemstones. The ruby is assigned to the planets Mars and Pluto. The esoteric movement revived the ancient belief and the gem industry made it another marketing tool to promote certain gems.
The healing powers of gems remain a controversial issue, but are mentioned for centuries by healers, shamans and medicine men. Whether it’s a fact or a placebo effect doesn’t matter, if it helps. The safest approach is to wear the gemstone in skin contact to the troubled part of the body. Ruby is said to be a general health protection and a help for backache and toenail problems.