A cut ruby.

Natural occurrence

Rubies have historically been mined in Thailand, the Pailin and Samlot provinces of Cambodia, and Afghanistan. Rubies were rarely found in Sri Lanka where pink sapphires are more common.


A naturally occurring ruby crystal

After the Second World War new ruby deposits were found in Tanzania, Kenya, Madagascar, Vietnam, Nepal, Tajikistan, and Pakistan. They have also been sometimes found in the U.S. states of Montana, North Carolina, and South Carolina. More recently, large ruby deposits have been found under the receding ice shelf of Greenland. The Mogok Valley in Upper Myanmar was for centuries the world main source for rubies. It has produced some of the finest rubies ever mined, but in recent years very few good rubies have been found there. The very best color in Myanmar (Burmese) rubies is sometimes described as “pigeon’s blood”. In central Myanmar the area of Mong Hsu also started to produce rubies during the 1990s and rapidly became the world’s main ruby mining area. The latest ruby deposit to be found in Myanmar is situated in Namya (Namyazeik) located in the northern Kachin state. In 2002 rubies were found in the Waseges River area of Kenya. Spinel, another red gemstone, is sometimes found associated with rubies from the same gem gravel or marble. Red spinel may be mistaken with ruby by people lacking experience with gems. However, fine red spinels may approach the average ruby in value.


Factors affecting value

Diamonds are graded using criteria that have become known as the four Cs, namely color, cut, clarity and carat weight. Similarly natural rubies can be evaluated using the four Cs together with their size and geographic origin.


Color: In the evaluation of colored gemstones, color is the single most important factor. Color divides into three components; hue, saturation and tone. Hue refers to “color” as we normally use the term. Transparent gemstones occur in the following hues: red, orange, yellow, green, blue, violet, purple and pink are the spectral hues. The first six are known as spectral hues; the last two are modified spectral hues. Purple is a hue that falls halfway between red and blue and pink is a paler shade of red. In nature there are rarely pure hues so when speaking of the hue of a gemstone we speak of primary and secondary and sometimes tertiary hues. In ruby the primary hue must be red. All other hues of the gem species corundum are called sapphire. Ruby may exhibit a range of secondary hues. Orange, purple, violet and pink are possible.


The finest ruby is best described as being a vivid medium-dark toned red. Secondary hues add an additional complication. Pink, orange, and purple are the normal secondary hues in ruby. Of the three, purple is preferred because, firstly, the purple reinforces the red making it appear richer. Secondly, purple occupies a position on the color wheel halfway between red and blue. In Burma where the term pigeon blood originated, rubies are set in pure gold. Pure gold is, itself a highly saturated yellow. Set a purplish-red ruby in yellow and the yellow neutralizes its compliment blue leaving the stone appearing to be pure red in the setting.



A ruby is a pink to blood-red gemstone, a variety of the mineral corundum (aluminium oxide). The red color is caused mainly by the presence of the element chromium. Its name comes from ruber, Latin for red. Other varieties of gem-quality corundum are called sapphires. The ruby is considered one of the four precious stones, together with the sapphire, the emerald, and the diamond.


Prices of rubies are primarily determined by color. The brightest and most valuable “red” called pigeon blood-red, commands a huge premium over other rubies of similar quality. After color follows clarity: similar to diamonds, a clear stone will command a premium, but a ruby without any needle-like rutile inclusions will indicate that the stone has been treated. Cut and carat (size) also determine the price.


Rubies have a hardness of 9.0 on the Mohs scale of mineral hardness. Among the natural gems only moissanite and diamond are harder, with diamond having a Mohs hardness of 10.0 and moissonite falling somewhere in between corundum (ruby) and diamond in hardness. Ruby is α-alumina (the most stable form of Al2O3) in which a small fraction of the aluminum3+ ions are replaced by chromium3+ ions. Each Cr3+ is surrounded octahedrally by six O2- ions.


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