Home > Ruby (corundum) (Molecule of the Month for March 1997 )

Picture of Ruby (corundum)

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Picture of Ruby (corundum)

Ruby has been the world's most valued gemstone for thousands of years. Ruby was said to be the most precious of the twelve stones God created when he created all things and this "lord of gems" was placed on Aaron's neck by God's command. The bible says that wisdom is "more precious than rubies," that is to say very valuable indeed. In the ancient language of Sanskrit, ruby is called ratnaraj, or "king of precious stones" and ratnanayaka, "leader of precious stones."

In fact, rubies are today still more valuable and rare than even the top quality colorless diamonds. The record price for a ruby sold at auction is a 16 carat ruby which sold for US$227,301 per carat at Sotheby's in 1988. A 27.37 carat Burmese ruby ring sold for US$4 million at Sotheby's in Geneva in May 1995, or $146,145 per carat. A 32 carat ruby sold for US$144,000 per carat at Sotheby's in 1989. In contrast, eight D-color internally flawless diamonds over 50 carats have been sold in the past six years and the largest, a pear-shape of 102 carats, fetched a mere US$125,000 per carat. Top rubies are so rare even the world's top gem dealers must incessantly comb estate sales and auctions to find them. Sizes above five carats are particularly rare.

Ruby is the gem quality of the mineral corundum, one of the most durable minerals which exists, a crystalline form of aluminium oxide. Corundum has a hardness of 9 on the Mohs scale and is also extremely tough. In its common form, it is even used as an abrasive.

The most famous source of fine rubies is Burma, which is now called Myanmar. The ruby mines of Myanmar are older than history: stone age and bronze age mining tools have been found in the mining area of Mogok. Rubies from the legendary mines in Mogok often have a pure red color, which is often described as "pigeon's-blood" although that term is more fanciful than an actual practical standard in the trade today. Myanmar also produces intense pinkish red rubies which are also vivid and extremely beautiful. Many of the rubies from Burma have a strong fluorescence when exposed to ultraviolet rays like those in sunlight, which layers on extra color. Burma rubies have a reputation of holding their vivid color under all lighting conditions.

Since demand for fine rubies is really only limited by the tiny supply available, new sources are always treated as exciting news in the trade. The most recent news is an exciting new mining area in Burma called Mong Hsu.

The new Mong Hsu ruby deposit is producing commercial quantities of commercial quality Burma ruby and also significant quantities of fine quality Burma ruby, particularly in sizes up to a carat. Burma ruby is now more readily available than Thai ruby, due to the new ruby rush in the area.

The new deposit has also affected the world capital of the ruby business: Thailand. Many of the ruby traders and cutters from Chanthaburi and Bo Rai have moved to Mae Sai in Thailand. In Tachilek in Myanmar, across the border from Mae Sai, a flourishing trade in Mong Hsu ruby has transformed a village into a prosperous town. Most Mong Hsu ruby is cut and marketed in Thailand.

Thailand is the world's most important ruby trading center. Perhaps 80 percent of the world's ruby goes through Thailand at some point in the trading cycle. The largest ruby cutting factories are in the Chanthaburi area of Thailand. Bangkok is generally where the world's buyers come to purchase ruby.

In 1992, a new ruby mine was discovered in Vietnam that produces rubies which are very similar to rubies from Burma. In fact, the geology of the new mine may be a continuation of the same formation that produced the Burma deposits. Some of the new Vietnamese rubies have been praised by experts as being virtually indistinguishable from top quality Burmese stones.

Fine rubies are also found in Thailand. Thai rubies tend to be darker red in tone: a real red, tending toward burgundy rather than pink, as Burma rubies do. This makes them very popular in the United States where consumers generally prefer their rubies to be a darker red rather than a darker pink. Some Thai rubies have black reflections, a phenomenon called extinction, which can make their color look darker than it really is. But Thai rubies also can have a rich vivid red that rivals the Burmese in intensity. Sri Lankan rubies can also be very beautiful. Sri Lankan stones are often pinkish in hue and many are pastel in tone. Some, however, resemble the vivid pinkish red hues from Burma.

Rubies from Kenya and Tanzania surprised the world when they were discovered in the sixties because their color rivals the world's best. Unfortunately, most of the ruby production from these countries has many inclusions, tiny flaws which diminish transparency. Rubies from the African mines are rarely transparent enough to facet. However, their fantastic color is displayed to full advantage when cut cabochon style. A few rare clean stones have been seen which are top quality.

Occasionally a few fine top-quality rubies appear on the market from Afghanistan, Pakistan, or the Pamir Mountains of the Commonwealth of Independent States. The terrain in these areas has made exploration for gemstones very difficult but someday they may produce significant quantities for the world market.

The most important factor in the value of a ruby is color. The top qualities are as red as you can imagine: a saturated pure spectral hue without any overtones of brown or blue. The word red is derived from the latin for ruby, ruber, which is derived from similar words in Persian, Hebrew, and Sanskrit. The intensity of color of a fine ruby is like a glowing coal, probably the most intensely colored substance our ancestors ever saw. It is no wonder they ascribed magical powers to these fires that burned perpetually and never extinguished themselves.

All colors of corundum except red are known as sapphires, which has created controversy about where ruby ends and sapphire begins, particularly in pink shades of corundum. In 1991, the International Colored Gemstone Association ruled that the lighter shades of the reddish hues of corundum should be included in the category of ruby.

After color, the other factors which influence the value of a ruby are clarity, cut, and size. Rubies that are perfectly transparent, with no tiny flaws, are more valuable than those with inclusions which are visible to the eye. Cut can make a big difference in how attractive and lively a ruby appears to the eye. A well-cut stone should reflect back light evenly across the surface without a dark or washed-out area in the center that can result from a stone that is too deep or shallow. The shape should also be symmetrical and there shouldn't be any nicks or scratches in the polish. Rubies and other gemstones are sold per carat, a unit of weight equal to one-fifth of a gram. Larger rubies, because they are more rare, will cost more per carat than smaller stones of the same quality.

Ruby sometimes displays a three-ray, six-point star. These star rubies are cut in a smooth domed cabochon cut to display the effect. The star is best visible when illuminated with a single light source: it moves across the stone as the light moves. This effect, called asterism, is caused by light reflecting off tiny rutile needles, called "silk," which are oriented along the crystal faces.

The value of star rubies and sapphires are influenced by two things: the intensity and attractiveness of the body color and the strength and sharpness of the star. All six legs should be straight and equally prominent. Star rubies rarely have the combination of a fine translucent or transparent color and a sharp prominent star. These gems are valuable and expensive.

Formal Chemical Name (IUPAC)

Update by Karl Harrison
(Molecule of the Month for March 1997 )