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Roger Weller, geology instructor                     

Shawn Kellerman
Physical Geology
Fall 2005





What is a Ruby ?

Ruby is red corundum, all other color varieties of corundum being referred to as sapphire. The ruby color range includes pinkish, purplish, orangey, and brownish red depending on the chromium and iron content of the stone. The trace mineral content tends to vary with the geologic formation which produced the ruby, so original place designations such as Burmese and Thai have come in later years to be sometimes used in describing color.


All corundum gems including ruby 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, especially by dissolving "silk" ; but it 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 indistinguishable from Nature's own heating processes, and stable, is acceptable -- as long as it is disclosed. For this reason such enhancement does not radically lower the value of ruby gems. Not so for other more recently invented treatments such as diffusion coloring, or polymer or glass filling.


Famous Rubies


A few rubies have distinguished themselves because of their size or extraordinary beauty and are being guarded for posterity The Louvre in Paris houses the Anne of Brittany Ruby, a 105-carat polished but irregular gem. The 167-carat Edwards Ruby was donated to the British Museum of Natural History in 1887 by John Ruskin. This 167-carat gem was named in honor of Major-General Sir Herbert Benjamin Edwards (1819-68) who saved British rule in India during the years of the Indian Mutiny. Two star rubies are displayed in American museums. The Smithsonian displays the 137-carat Rosser Reeves Ruby, and the American Museum of Natural History has the 100-carat Edith Haggin de Long Ruby.



Star Rubies


Some rubies display a luminous star when viewed in the right light. This is caused by the orientation of intersecting needles within the stone. The light reflecting off them forms a star. Stars may be seen on certain translucent stones that have been cut in a dome shape.



The Six Reminders of buying Rubies



Look for the best rubies at a trusted and well-respected jewelry store. Be sure the store stocks a good variety of rubies and that the staff is knowledgeable about gemstones in general and rubies in particular.



Ask if the stone has been treated in any way. Some common treatments to enhance gems include irradiation, heat treatment, dyeing and coating. Not all of these treatments will devalue the stone, but always ask so you know what you're getting.



Examine the color of the ruby. The best stones are pure red with a fiery intensity. You will see no inclusions in a perfect, transparent ruby.



Study the cut of the ruby. Hold the stone face up, and be sure the light reflects evenly from the surface. The center of the stone should not appear dark, and there should be no scratches on the surface. Look at the stone from several different angles to be sure.



Keep in mind that because large rubies are so scarce, you may not be able to find a stone larger than five carats. Larger rubies generally cost more per carat than smaller rubies.



Compare several rubies side by side. Look at the color and the cut of each, and decide on your favorite.



Basic information



Ruby is hard (9) and tough, making it a superb jewelry stone.  For reasonably clean stones, no special wear or care precautions are necessary. Ruby shows pleochroism which means that the color varies with the direction of viewing. Most stones show purplish red and orangey red, although the presence or absence of trace minerals can dampen either of these. The overall color can often, but not always, give a clue to a stone's geographic origin, with Burmese stones tending to purplish red colors and Thai stones appearing more brownish red. In addition, 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, and are greatly admired. Thai stones generally lack this property. Although Asia has historically been the major producer of ruby gems, there are many other sources including the USA, Australia, and most recently Africa.




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, making even these smaller stones relatively high in value.
Stones of Burmese origin generally command the highest prices. The vast majority of rubies are "native cut" in the 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, and my own bias is that they are worth it.


Sinkankas and Miller in the Standard Catalog of Gem Values, 2nd. Ed. lists 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 maximum.


Burmese stones in 1/2 to 1 ct sizes with slightly purplish red color and light inclusions range from $300 to $3000/ ct, for example. The price survey done by the International Gem Society reports that clean, top color gems in the 1/2 to 1 ct size range are being sold, retail, on the Internet with a range of $1000 - $3000/ct.




Works Citied