Ruby

From Wikipedia, the free encyclopedia

For other uses, see Ruby (disambiguation).

Ruby
Ruby crystal before faceting, length 0.8 inches (2 cm).
General
Category	Mineral
Chemical formula	aluminium oxide with chromium, Al2O3::Cr
Identification
Color	Red, may be brownish
Crystal habit	Varies with locality. Terminated tabular hexagonal prisms.
Crystal system	Trigonal
Cleavage	No true cleavage
Fracture	Uneven or conchoidal
Mohs Scale hardness	9.0
Luster	Vitreous
Refractive index	~1.77
Pleochroism	?
Streak	white
Specific gravity	4.0
Fusibility	perfectly
Solubility	?
Major varieties
Pink sapphire	Caused by a color impurity and makes the stone appear pink.

Ruby is a red gemstone, a variety of the mineral corundum (aluminium oxide) in which the color is caused mainly by chromium. Its name originates from ruber or rubrum, Latin for red. Natural rubies are exceptionally rare, though artificial ones (sometimes called created ruby) can be manufactured by the Verneuil process relatively inexpensively. Other varieties of gem-quality corundum are called sapphires.

Rubies are mined in Africa, Asia, Australia, and Greenland. They are most often found in Myanmar, Sri Lanka, Kenya, Madagascar and Thailand, though they have also been found in the U.S. states of Montana, North Carolina and South Carolina. The Mogok Valley in Myanmar has produced some of the finest rubies. However in recent years very few good rubies have been found there. In central Myanmar the area of Mong Hsu also produces rubies. In 2002 rubies were found in the Waseges River area of Kenya. Rubies are being mined at Audilamena in northeastern Madagascar. Sometimes spinels are found along with rubies in the same geological formations and are mistaken for the more valuable gem. However, fine red spinels may approach the average ruby in value.

Rubies have a hardness of 9 on the Mohs scale of mineral hardness, and among the natural gems are only surpassed by diamonds in hardness.

Ruby gemstones are valued according to several characteristics including size, color, clarity and cut. All natural rubies have imperfections in them, including color impurities and inclusions of rutile needles known as silk. If the silk inside of the stone is absent, then one could assume that the stone was heated at a temperature of 3000 degrees, which is done to give the ruby a better color of red. Usually the rough stone is heated before cutting. On the other hand, artificial rubies may have no imperfections. 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 is suspected of being artificially made and its status as a priceless gem is therefore not completely assured. Some manufactured rubies have dopants added to them so that they can be identified as artificial, but most require gemological testing to determine their origin. Rubies come in various shades of red, red purple and red orange. A medium toned red or red with slight blue is most desired. Clarity of the stone and inclusions are also taken into account to determined the stones value. Once the stones looks more toward the color purple or orange then it is called a fancy sapphire.

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

Rubies occasionally show asterism when cut into a cabochon. When they show this, they are referred to as "star rubies." They can sometimes be more valuable than normal rubies because asterism is rare.

The world's biggest ruby is the Rajaratna Ruby, which weighs 2,475 carats (495 g). Because the Rajaranta shows asterism, it is also the largest star ruby. The world's biggest double-star ruby (with a 12-pointed star) is the Neelanjali Ruby, weighing 1,370 carats (274 g). Both rubies currently belong to G. Vidyaraj from Bangalore, India. A 8.62 ct. Burmese ruby sold for $ 425,000 per carat (2,125,000 $/g) or $ 3,800,000 on Feb. 15, 2006 at Christie's in Switzerland.