Ruby (Rubies)
Burma (Myanmar) is famous for producing the greatest amount of top quality ruby with a fine, clear, deep-red color. Most of the best quality ruby comes from the Mogok Valley in Burma and others from newer sources such as Mong Shu (discovered in the Shan State in 1991), and Namya, in the Kachin State, which experienced a rush in 2000. ?Pigeon blood? was once the paramount color for ruby but this appellation is now tricky as there is no standard behind it.Ruby can be true red or red with some purple or orange overcast or going towards pink. On the last point, the fact is that ruby and pink sapphire are basically the same stone as they are both aluminum oxide with a small amount of chromium. High levels of chromium give red, lower concentrations give pink. There is no clear and worldwide-accepted borderline between what is a ruby vs. a pink sapphire. Rubies in Mogok and Mong Shu are found either in marble primary deposits in the mountains around the valley or in alluvial placers in the valley.
In Namya they are exclusively found in alluvial deposits in this swamp area. All Burmese rubies were born from a metamorphic process (as well as Vietnamese, Nepalese and Afghan stones). They are usually poor in iron, and as a result, show a strong red fluorescence which make them different from their cousins from basaltic deposits in Thailand or Africa. Rubies usually occur in Burma as tabular crystals with hexagonal prisms. Usually the basal plane shows markings consisting of striations, often as equilateral triangles, and prisms are commonly striated horizontally. Mogok also produces some more rare ruby crystals in which rhombohedrons are so well developed that the stone looks similar to a spinel crystal. For many centuries red spinels and rubies were associated with one another and believed to be the same stone.
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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.
Physical properties
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 ?-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. This crystallographic arrangement strongly affects each Cr3+, resulting in light absorption in the yellow-green region of the spectrum and thus in the red color of the gem. When yellow-green light is absorbed by Cr3+, it is re-emitted as red luminescence. This red emission adds to the red colour perceived by the subtraction of green and violet light from white light, and adds luster to the gem's appearance. When the optical arrangement is such that the emission is stimulated by 694-nanometer photons reflecting back and forth between two mirrors, the emission grows strongly in intensity. This effect was used by Theodore Maiman in 1960 to make the first successful laser, based on ruby.
All natural rubies have imperfections in them, including color impurities and inclusions of rutile needles known as "silk". Gemologists use these needle inclusions found in natural rubies to distinguish them from synthetics, simulants, or substitutes. Usually the rough stone is heated before cutting. Almost all rubies today are treated in some form, with heat treatment being the most common practice. However, rubies that are completely untreated but still of excellent quality command a large premium.
Some rubies show a 3-point or 6-point asterism or "star". These rubies are cut into cabochons to display the effect properly. Asterisms are best visible with a single-light source, and move across the stone as the light moves or the stone is rotated. Such effects occur when light is reflected off the "silk" (the structurally oriented rutile needle inclusions) in a certain way. This is one example where inclusions increase the value of a gemstone. Furthermore, rubies can show color changes — though this occurs very rarely —; as well as chatoyancy or the "cat's eye" effect.
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.
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.