D4888 Brilliant cut rubies & Pink Mother of Pearl in quartz set in White 18K gold	D4887 Brilliant cut rubies & Pink Mother of Pearl in quartz set in White 18K gold	D2808 18K gold setting with Pave of white diamonds and rubies	D4453 White brilliant cut diamonds pave setting & Rubies in  flower shaped forms on 18K white gold
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Ruby is a red gemstone that varies from a light pink to a blood red, a variety of the mineral corundum (aluminum oxide). The color is caused mainly by chromium. Its name comes from ruber, Latin for red. Natural rubies are exceptionally rare, but synthetic rubies (sometimes called created ruby) can be manufactured fairly cheaply. Other varieties of gem-quality corundum are called sapphires. It is considered one of the four precious stones, together with the sapphire, the emerald and the diamond.

Rubies are mined in Africa, Asia, Australia, Greenland, Madagascar and North Carolina. They are most often found in Myanmar (Burma), Sri Lanka, Kenya, Madagascar, and Cambodia, but they have also been found in the U.S. states of Montana, North Carolina and South Carolina. The Mogok Valley in Upper Myanmar has produced some of the finest rubies but, in recent years, very few good rubies have been found there. The unique color in Myanmar (Burmese) rubies is described as "pigeon’s blood". They are known in the trade as “Mogok” rubies. In central Myanmar the area of Mong Hsu also produces rubies. The latest ruby deposit to be found in Myanmar is situated in Nam Ya. In 2002 rubies were found in the Waseges River area of Kenya. Sometimes spinels are found along with rubies in the same rocks and are mistaken for rubies. However, fine red spinels may approach the average ruby in value.

Rubies have a hardness of 9.0 on the Mohs scale of mineral hardness. Among the natural gems only diamond is harder (Mohs 10.0 by definition).

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, stimulants, or substitutes. Usually the rough stone is heated before cutting. Almost all rubies today are treated in some form (of which heat treatment is the most common practice), and rubies which are completely untreated and still of excellent quality command a large premium. In general we can list the following types of improvements: color alteration, improving transparency by dissolving rutile inclusions, healing of fractures (cracks) or even completely filling them. See Treatments below.

Prices of rubies are primarily determined by color (the brightest and best "red" called Pigeon Blood Red, command 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 the stone has been treated one way or another. Cut and Carat (size) also determine the price approximately like clarity does.

Phenomena

Sometimes rubies show a 3-point or 6-point star. These Rubies are cut into cabochons to display the effect properly. Stars are best visible with a single-light source, and move across the stone as the light moves. Such effects are called asterism and occur when light is reflected off the silk (the rutile inclusions) in a certain way. This is one example where inclusions actually increase the value of a gemstone. Rubies can furthermore show color changes — though this occurs very rarely — and chatoyancy, (having a changeable luster).

Treatments

Improving the quality of gemstones, and thus treating them, has been a practice of all ages. The level of treatment however can differ considerably and impact the price of a gemstone accordingly. Some treatments occur in almost all cases and are (therefore) considered "acceptable" practices. As with most gemstones, the most accepted and most occurring treatment is heat treatment. Although heat treatment affects the price of a top quality ruby, most if not all rubies at the lower end of the market are heat treated. Heat treatment is performed on the rough stones to improve color, remove purple tingle, blue patches and silk. These heat treatments typically occur around temperatures of 1800°C (3272°F).^[1] Some rubies undergo a process of low tube heat, when the stone is heated over charcoal of a temperature of about 1300°C (2372°F) for 20 to 30 minutes. The silk is only partially broken as the color is improved.

A less acceptable treatment, and one which has gained notoriety in recent years is "Lead Glass Filling" of Rubies. By filling the fractures inside the ruby with so-called "lead glass" the transparency of the stone is dramatically improved making previously unsuited rubies now fit for applications in jewelry. The process is typically split into 4 steps:

1. Rough stones are pre-polished to eradicate all surface impurities that may affect the process

2. Rough is cleaned with Hydrogen Fluoride

3. First heating process whereby no fillers are added. The heating process eradicates impurities inside the fractures. Although this can be done at temperatures up to 1400°C (2552°F) it most likely occurs at a temperature of around 900°C (1636°F) since the Rutile silk is still intact

4. Second heating process in an electrical oven with different chemical additives. Different solutions and mixes have shown to be successful, however mostly lead-containing glass-powder is used at present. The Ruby is dipped into oil, then covered with powder, embedded on a tile and placed in the over where it is heated at around 900°C (1636°F) for one hour in an oxidizing atmosphere. The Orange colored powder transforms upon heating into a transparent to yellow-colored paste, which fills all fractures. After cooling the color of the paste is fully transparent, that dramatically improves the overall transparency of the Ruby.

In case a color needs to be added, the glass powder can be "enhanced" with Copper or other Metal Oxides as well as elements such as Sodium, Calcium, Potassium etc.

The Second heating process can be repeated three to four times consecutively, even applying different mixtures.

Synthetic and imitation rubies

Synthetic rubies have been made since the late 19th century. They have become more common since the work of Auguste Verneuil and the introduction of the flame fusion process. Other processes in which synthetic rubies can be produced are through the Pulling process, flux process, and the hydrothermal process. Most synthetic rubies originate from flame fusion, due to the low costs involved. Synthetic rubies may have no imperfections visible to the naked eye but magnification may reveal curves striae and gas bubbles. The fewer the number and the less obvious the imperfections, the more valuable the ruby is; unless there are no imperfections (i.e., a "perfect" ruby), in which case it will be suspected of being artificial. Dopants are added to some manufactured rubies so they can be identified as synthetic, but most need gemological testing to determine their origin. Imitation rubies have also been present in the gemstone market for some time. Red spinel, red garnet and even glass have been falsely named as rubies. Trade terms such as balas ruby for red spinel and rubellite for red tourmaline can mislead unsuspecting buyers. Such terms are therefore discouraged from being used by many gemological associations such as the Gemological Institute of America (GIA).

Records

Although pieces of red corundum can be found weighing many kilograms, they are generally not of sufficient quality to be valuable as gemstones. For this reason, auction prices are the best indicator of a stone's true value, and prices do not necessarily correlate with size. As of 2006, the record price paid at auction for a single stone was $5,860,000 for an unnamed 38.12 carat cabochon-cut ruby.  However, other stones with potentially greater value may never have been sold at auction.

Information courtesy of Wikipedia.org