Ruby
- This article is about the mineral. For other uses of the term, see Ruby (disambiguation).
| Ruby | |
|---|---|
 Ruby crystal before faceting, length 0.8 inches (2 cm) |
|
| General | |
| Category | Mineral |
| Chemical formula | aluminum oxide with chromium, Al2O3::Cr |
| Identification | |
| Color | Red, may be brownish or purplish |
| Crystal habit | Varies with locality. Terminated tabular hexagonal prisms. |
| Crystal system | Hexagonal |
| Cleavage | No true cleavage |
| Fracture | Uneven or conchoidal |
| Mohs Scale hardness | 9.0 |
| Luster | Vitreous |
| Refractive index | ~1.762-1.770 |
| Pleochroism | Orangy Red, Purplish Red |
| Streak | white |
| Specific gravity | 4.0 |
| Fusibility | perfectly |
| Major varieties | |
| Pink sapphire | Caused by a color impurity and makes the stone appear pink. |
Ruby (from the Latin word ruber, meaning "red") is a highly valued red gemstone. It is a variety of the mineral corundum (aluminum oxide), with the red color produced mainly by the presence of chromium. The non-red varieties of gem-quality corundum are called sapphires.
The ruby is considered one of the four most precious gems, the other three being sapphire, emerald, and diamond. Natural rubies are exceptionally rare, but synthetic rubies (sometimes called "created rubies") can be manufactured fairly inexpensively.
Occurrence
Most rubies have been found in Myanmar (Burma), Sri Lanka (Ceylon), Kenya, Madagascar, and Thailand. They have also been mined in Australia and Greenland. In the United States, they have been found in Montana, North Carolina, and South Carolina.
The Mogok Valley in Myanmar is well-known for having produced some of the finest rubies. In recent years, however, very few good rubies have been found there. Other ruby-producing areas of Myanmar are Mong Hsu and Nam Ya. In 2002, rubies were found in the Waseges River area of Kenya. In addition, rubies are being mined at Audilamena in northeastern Madagascar. Sometimes, red spinels are found in the same rocks as rubies and are mistaken for the latter. Nonetheless, fine red spinels may approach the average ruby in value.
Characteristics
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 their size, color, clarity, and cut. All natural rubies have imperfections in them, including color impurities and inclusions of rutile needles known as "silk". The absence of silk in the stone indicates that the stone was heated to a temperature of up to 1800 °C in an oven, to enhance the red of the ruby.
Today, about 90% of all rubies are heated. Usually, the rough stone is heated before cutting. Rubies that are not heated are considered unusual. Some rubies undergo a process of low tube heat—that is, the stone is heated over charcoal at a temperature of about 1300 °C for 20 to 30 minutes. The silk is partially broken and the color is improved.
Asterism and chatoyancy
Rubies occasionally show an internal, star-like formation called asterism, when cut into a cabochon.[1] These are called "star rubies" and, because asterism is rare, they can be more valuable than regular rubies. On rare occasions, rubies show color change and chatoyancy—an optical reflectance that arises either from the fibrous structure of a material or from fibrous inclusions or cavities in the stone.
Synthetic and imitation rubies
Synthetic rubies have been made since the late nineteenth century. They have become more common since the work of Auguste Verneuil and the introduction of the flame fusion process. They can also be produced by other methods, such as the Pulling process, flux process, and hydrothermal process. Most synthetic rubies are produced by flame fusion, because of the low costs involved.
Synthetic rubies may have no imperfections visible to the naked eye but magnification may reveal curved striae and gas bubbles. The fewer and less obvious the imperfections, the more valuable the ruby is. If, however, there are no imperfections (i.e., a "perfect" ruby), the ruby 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, including the Gemological Institute of America (GIA).
Identifying synthetic rubies
Most synthetic rubies can be identified only by using a microscope or loupe with at least a 10x magnification, or with a light source, such as a lamp or penlight. Occasionally, a technique relying on fluorescence is used to differentiate between a synthetic ruby and a natural one.
Rubies produced by the flame fusion process:
- show curved growth lines;
- may also show included gas bubbles.
Rubies produced by the Pulling process:
- show curved growth lines.
Rubies produced by the flux process:
- are translucent to opaque, with included crystals or liquids;
- may have wispy veils (cloud-like structure in the ruby);
- may have wavy, fingerprint-like inclusions.
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.[1] However, other stones with potentially greater value may never have been sold at auction.
Trivia
- The ruby symbolizes passionate love.
- It is the birthstone associated with the month of July.
- It is the most commonly named precious stone in the Bible. For example, Proverbs 31: states, "A virtuous wife is worth more than rubies."
- According to Rebbenu Bachya, the word odem in the book of Exodus, verse 28:17, means "ruby". It was the stone on the Ephod representing the tribe of Reuben. Modern Hebrew has taken this meaning.
- A synthetic ruby crystal was used to create the first laser.
- The famous lighted "Red Stars" mounted above the Kremlin spires, once thought to be giant rubies mined in Siberia, are actually colored glass.[2]
- Although their names bears some similarity, rubies are not related to the chemical element rubidium and do not contain rubidium. Both names derive from the same Latin word, ruber, describing their reddish color.
See also
Footnotes
ReferencesISBN links support NWE through referral fees
- Hurlbut, Cornelius S.; Klein, Cornelis (1985). Manual of Mineralogy (20th ed.). New York: John Wiley and Sons. ISBN 0-471-80580-7
- Weinstein, Michael (1958). The World of Jewel Stones. Sheriden House.
- Nassau, Kurt (1980). Gems made by man. Gemological Institute of America. ISBN 0-87311-016-1
Credits
New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:
The history of this article since it was imported to New World Encyclopedia:
Note: Some restrictions may apply to use of individual images which are separately licensed.
