Rubies are one of the most popular gems for good reasons. As gem-quality examples of the mineral corundum, they are exceptionally durable and one of the few gem species whose color reaches vivid saturation levels. Fine quality rubies are some of the most expensive gems, with record prices over $100,000 per carat. Accurately grading rubies requires knowing a great deal about them, and there is a great deal to know about them. Synthetic ruby can be created by several different methods, including flame fusion, the Czochralski process, flux, and hydrothermal. Rubies are also subjected to more treatments than almost any other gem.
Rubies are the most valuable members of the corundum family. Large gem-quality rubies can be more valuable than comparably sized diamonds and are certainly rarer. There is a relative abundance of smaller, 1-3 carat blue sapphires compared to the scarcity of even small gem-quality rubies. As a result, even these smaller stones are relatively high in value. Anna Miller and John Sinkankas in their work, Standard Catalog of Gem Values, 2nd. Ed., list a wide range of wholesale prices for faceted gem rubies. Prices are dependent on origin, color, size, and clarity: from a low of $100 to $15,000/ct. Myanmar or Burmese stones in ½ to 1 carat sizes with slightly purplish red color and light inclusions range from $300 to $3,000/ct., for example. The price survey done by the International Gem Society reports that clean, top-color gems in the ½ to 1 carat size range are being sold at retail with a range of $1,000-$3,000/ct. The vast majority of rubies are “native cut” in their country of origin. High-value ruby rough is tightly controlled and rarely makes its way to custom cutters. Occasionally, such native stones are recut to custom proportions, albeit at a loss of weight and diameter. Custom cut and recut stones are usually more per carat.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Is a Variety of||Corundum|
|Varieties||Flux-Grown Ruby, Geneva Ruby, Star Ruby, Verneuil Ruby|
|Refractive Index||1.757 - 1.779|
|Colors||All varieties of red, from pinkish, purplish, orangey, brownish, to dark red.|
|Luster||Vitreous to adamantine|
|Polish Luster||Vitreous to subadamantine|
|Specific Gravity||3.99 - 4.1, usually near 4|
|Luminescence||Myanmar stones fluoresce intensely, red, in SW, LW, and X-rays. Red fluorescence is, however, not diagnostic of country of origin or natural origin. Thai ruby fluoresces weak red in LW, weak or none in SW. Sri Lankan ruby fluoresces strong orange-red in LW, pink (moderate) in SW. Flame Fusion: very strong in LW, orange/red, moderate to strong in SW, orange/red. Flux Grown: strong in LW, orange/red, moderate to strong in SW, orange/red. (May have blue over tint)|
|Spectral||A distinctive spectrum; a strong red doublet at 6942/6928 is notable, and this may reverse and become fluorescent. Weaker lines at 6680 and 6592. Broad absorption of yellow, green, and violet. Additional lines seen at 4765. 4750, and, 4685. (The reversible fluorescent doublet is a sensitive test for the presence of chromium in a corundum. Even mauve and purple sapphires have a trace of Cr and show these lines.)|
|Enhancements||Heat treated. Common. Fracture-filled, occasional.|
|Special Care Instructions||None|
|Transparency||Transparent to opaque|
|Formula||Al2O3 + Cr|
|Pleochroism||Strong: purplish red/orangey red. (Trace minerals can dampen this effect).|
|Optics||RI: o = 1.757-1.770; e = 1.765-1.779 (usually 1.760, 1.768); Uniaxial (-)|
|Etymology||From the Latin ruber for red.|
|Occurrence||Metamorphosed crystalline limestones and dolomites, as well as other metamorphic rock types such as gneiss and schist. Also, igneous rocks such as granite and nepheline syenite.|
|Inclusions||Natural rubies: silk, rutile needles, usually crossing at a 60 degree angle. Zircon crystals with halo of dark fractures, fingerprints, hexagonal growth lines, color zoning. Synthetic rubies: see "Synthetics" below.|
Ruby is red corundum. The color comes from traces of chromium. All other color varieties of corundum are referred to as sapphire. Depending on the chromium and iron content, rubies have a color range that includes pinkish, purplish, orangey, and brownish reds. The trace mineral content tends to vary with the location of the geologic formation which produced the ruby. This is why terms like “Burmese” (Myanmar) or “Thai” (Thailand) are sometimes used to describe the color of stones from those locations. (However, color is not always an indication of origin).
There is an old joke about questionable stones: whether it’s a ruby or a pink sapphire depends on whether you’re the buyer or the seller. Most authorities expect a medium to medium dark-red color tone in a ruby. Stones lighter than this are called pink sapphire. However, there is no general agreement on how to draw the line between rubies and sapphires.
Few other gems have as much myth, lore, and romance surrounding them as rubies. One of their chief attractions is the alleged protection from misfortune and bad health they were believed to afford their lucky owners. As the science of gemology developed, many historically important rubies, such as the famed Black Prince’s Ruby of the British crown jewels, were determined to be other red gems, most often red spinels.
While high-quality ruby is usually faceted for jewelry, ruby rough of lower quality is used in great quantities to make beads, carvings, and other ornamental objects.
Overall color can often, but not always, offer a clue to a ruby’s origin. Stones from Myanmar (formerly Burma) tend to have purplish red colors. Thai stones tend to appear more brownish red. Rubies fluoresce in long or short wave ultraviolet light. This property can also often be used to help identify a stone’s geographic origin. Myanmar rubies often fluoresce so strongly that the effect is noticeable even in sunlight. They literally seem to glow and are greatly admired. Thai stones generally lack this property.
Rubies as well as sapphires can display asterism or the “star effect” due to rutile inclusions in a ruby’s hexagonal crystal matrix. If this rutile is sufficiently abundant and precisely arranged, proper cabochon cutting can create star rubies. Today there are heating and diffusion processes that can increase the rutile content and improve such gems.
Corundum gemstones, both rubies and sapphires, were first synthesized in the early 1900s by a simple flame fusion process. Many jewelers and gemologists have had the unpleasant task of telling the proud inheritors of their grandmothers’ treasured ruby rings or brooches that they contain flame fusion stones with more sentimental than commercial value.
More complex synthesis processes have been developed in recent years. These simulate natural formation conditions so closely that colors and even inclusions look extremely natural. Such stones are difficult for all but the most highly skilled professionals to identify as synthetic. See Synthetic Gemstones and Their Identification and Identifying Inclusions Found in Synthetic Gems for more information.
Rubies have a long history of enhancement. Unless the seller specifically states the stone is unheated, you should assume that some kind of heat treatment has been used. Usually high temperature heating and controlled cooling is done to clarify the stones. This process dissolves silk (rutile inclusions) and can also improve tone and saturation of color. Such treatments can only be detected in stones whose residual inclusions show signs of heat stress. Truly clean stones will give no clues and cannot be verified as natural color.
The general view at present seems to be that simple heating, being stable and indistinguishable from nature’s own heating processes, is acceptable as long as it is disclosed. For this reason, heating doesn’t radically lower the value of ruby gems. This is not the case for other more recently invented treatments, such as diffusion coloring or filling with polymer and/or lead glass.
For more information on ruby enhancements, see Corundum Treatments.
Although Asia has historically been the major producer of ruby gems, there are many other sources including the United States, Australia, and most recently Africa. Origin definitely affects the value of rubies.
Stones from Myanmar generally command the highest prices. They have the coveted, near perfect coloring known as “pigeon blood red,” which is a very slightly purplish red with vivid saturation and dark tone. They also have extreme red fluorescence. A mining tract in the Mogok region is the primary source of gem quality rubies. This fabled deposit has been known for over 1,000 years. It’s home to some of the finest rubies ever found. The color of Mogok rubies often occurs in rich patches and swirls. (Color zoning can occur occasionally). Mogok rubies hold color in virtually any lighting condition, which contributes to the demand for these gem-quality stones. The shape of Mogok ruby rough generally yields well-proportioned stones. In addition to faceted stones, Mogok also produces the world’s finest star rubies.
In the late 1990s, gem quality rubies began appearing in much more abundance from the Möng Hsu region of Myanmar. The rubies from Möng Hsu are a rich, fluorescent red and are easily distinguished by their dark core. These gems were often treated at very high temperatures to enhance their color. While conventional heat treatment is an accepted practice in the trade, the level of heat applied to Möng Hsu rubies in order to enhance their color led to some controversy in the industry. Concerns were raised not only regarding heat treatment more generally but also over whether rubies from Möng Hsu should be distinguished from other Myanmar rubies. There’s still no agreement amongst the trade on this matter.
Rubies have started to come out of Nanyazeik in Myanmar’s Kachin State. It’s too soon to tell if Nanyazeik will become an important source.
Some of the worlds finest rubies have come from Sri Lanka’s gem gravels. Top-grade Sri Lankan reds are virtually indistinguishable from their Mogok brethren, but most tend towards purple or pink. As with Sri Lanka sapphires, color accumulates in large stones. Stones of five carats or more can be quite magnificent. Due to the bi-pyramidal shape of the rough, many stones are cut with overly-deep pavilions. Sri Lankan ruby is strongly fluorescent and star stones are common.
Known in olden times as the Beryl Island, Madagascar was long considered mineralogical nirvana. It’s still known for its gem wealth. Madagascar produces mainly fine blue and pink sapphires. Two important ruby deposits have also been discovered. The first is approximately 1030 km inland from the coastal town of Vatomandry. The second is roughly 4570 km from the town of Andilamena. Vatomandry is said to produce the better-quality stone, being lighter and brighter (more reminiscent of Myanmar), while the Andilamena stone is somewhat darker and not as clean. Rutile silk seen in some pieces suggests that star stones may be forthcoming. Much of the material from both deposits is heat-treated.
Stones from Kenya and Tanzania are magnificent when clean, but facet-grade material is rare. Like Myanmar, much of this material is strongly fluorescent. Star stones are not produced from these deposits. Beginning in the mid-1990s, mines near Songea began to produce material with a dark, garnety color veering towards orange. While this material is ruby of a sort, it is marginal due to its high iron content.
The Jegdalek deposit in Afghanistan has produced rubies that rank with fine Mogok stones, but facetable material is in short supply. Similar to Vietnamese rubies, many of these stones contain small areas of blue color. They are also strongly fluorescent. (If this deposit ever produces clean material, the market will be sure to take notice). Star stones are not produced here.
The main attraction of ruby from Thailand and Cambodia is its high clarity, but the flat crystal shapes generally yield overly shallow stones. Due to a high iron content, which quenches fluorescence, most of these rubies tend to have a garnet-red color. These stones have a total lack of light-scattering silk inclusions, so star stones are not found here. (Although heat treatment does make improvements, it’s not enough). In Thai/Cambodian rubies, only those facets where light is totally internally reflected will be a rich red. The others appear blackish, as in red garnets. Thai stones are actually less purple than most Myanmar rubies. However, Myanmar-type rubies appear red all over the stone. (Not only is a rich red seen in the areas where total internal reflection occurs, but due to the red fluorescence and light-scattering silk, other facets are also red).
With the decline in Myanmar production during the 1962-1990 period, the market became conditioned to Thai/Cambodian rubies. Some people actually preferred them. Thai/Cambodian rubies are acceptable only when good material from the Myanmar-type sources is not available. Today, production from Thailand is zero and from Cambodia is negligible. Occasionally one might hear statements about how Cambodian stones are superior to those from across the border in Thailand. However, bear in mind that the deposits are essentially one that straddles the border.
Nepal is a relatively new source of rubies. A goat herder discovered ruby in the mountains in the 1980s. The clarity of Nepalese ruby is usually low to mid-commercial, although gemmy crystals do exist. Typically, Nepalese crystals are 5 carats or less. Color is often heavily zoned, pure red to pinkish-purplish red.
Vietnam had significant discoveries north of Hanoi in 1983 and in Luc Yen in 1987. Between November 1989 and March 1990, more than 3 million carats of ruby and pink sapphire were mined from one Vietnamese deposit. Word spread quickly in the trade that the color of the finest material was comparable with that of Myanmar. However, unlike the Mogok material, the clarity of Vietnamese ruby is mostly lower, with few eye-clean gems. The best Vietnamese ruby approaches fine Mogok, but, since the early 1990s, most have tended towards pink. Today, little facet-quality is produced. Even the cabochon material rarely competes with that available from Möng Hsu. Some pinkish star material is also produced.
For more information on rubies from these and other parts of the world, see our article on identifying the origins of rubies and sapphires.
- Cathedrale St. Guy (Prague): 250 carats.
- Narodni Museum (Prague): 27.11 carats (Mynamar).
- American Museum of Natural History (New York): 100 carats (de Long star ruby).
- British Museum of Natural History (London): ruby crystal of 690 grams (Myanmar).
- Smithsonian Institution (Washington, DC): 138.7-carat Rosser Reeves star ruby (red, Sri Lanka); 50.3-carat (violet-red star ruby, Sri Lanka); 33.8-carat (red star, Sri Lanka).
- Los Angeles County Museum (Los Angeles): Myanmar crystal, 196.1 carats.
- Iranian Crown Jewels: fine buckle of 84 Myanmar ruby cabs, up to 11-carat size.
- Historical rubies include: a 400-carat Myanmar rough that yielded 70 and 45 carat gems, a rough of 304 carats found about 1890, the Chhatrapati Manik ruby, and the 43-carat Peace Ruby.
Please note, these are descriptive terms. Rubies can’t always be identified by their color alone.
- African, usually orangish red.
- Beef Blood, slightly darker than pigeon blood.
- Burma or Oriental, red to slightly purplish red in medium dark tone with vivid saturation. (Also called “pigeon blood red”).
- Ceylon or Sri Lanka, lighter in tone, often more brilliant than Myanmar or Thai rubies.
- French or Cherry, slightly lighter than pigeon blood.
- Star Ruby, includes stones that are too light or too purple to call ruby if transparent.
- Thai or Siamese, dark red to brownish or purplish red.
- Synthetic star corundums were very popular in the 1950’s under the trade name “Linde Stars” and are still in production today.
Ruby’s hardness is second only to diamond among natural gems. This makes it a superb jewelry stone. Of course, a heavily included or fractured stone will be less stable. For reasonably clean stones, no special wear or care precautions are necessary. Consult our gemstone care guide for recommended cleaning methods.
by Barbara Smigel, PhD, GG, Artistic Colored Stones.; Dr. Joel Arem; Donald Clark, CSM IMG; Richard B. Drucker, GG, from his excellent 1999 article in JCK Magazine