Ruby is a red gemstone. Rubies can vary from a light pink to a blood red, a variety of the mineral corundum (aluminium 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 gems, 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.

Ruby gemstones are valued according to size, color, clarity and cut. 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. If there is no silk in the stone, that shows that the stone was heated to a temperature of up to 1800C (3272F) in an oven to give the ruby a better color of red. Usually the rough stone is heated before cutting. About 90% of all rubies today are heated, and rubies which are not heated are considered unusual. Some rubies undergo a process of low tube heat, when the stone is heated over charcoal of a temperature of about 1300C (2372F) for 20 to 30 minutes. The silk is partially broken and the color is improved. The fracture filling of rubies is also done intentionally, and it is not always disclosed to gem buyers. Glass-filling voids in rubies, without disclosure, is considered an unethical practice.

  • 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 gemmological 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.

  • Trivia
  • A synthetic ruby crystal was used to create the first laser.

    According to Rebbenu Bachya, the word odem in the verse Exodus 28:17 means "ruby"; it was the stone on the Ephod representing the tribe of Reuben. Modern Hebrew has taken this meaning.

    Ruby is also the most commonly named precious stone in the Bible; an example being Proverbs 31: "A virtuous wife is worth more than rubies."

    The famous lighted "Red Stars" mounted above Kremlin spires, thought to be giant rubies mined in Siberia, are actually colored glass.

    Ruby is the birthstone associated with July.

    Ruby is associated with the Sun in vedic astrology.

    Ruby symbolizes passionate love.

    Although their names bear some similarity, rubies are not related to rubidium, and they don't contain this chemical element. Both names derive from the same Latin word, ruber, meaning red, in reference to the red color of the ruby, and the red resonance line of rubidium vapor, respectively.