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Opal fact file | |
| Crystal Structure:octahedron Chemical Composition: Quartz – Silicon dioxide, SiO2 Hardness: 5 ½ to 6 ½ MOHS | Refractive Index: 1.43-1.46 Colors: Body color – white or tan or bluish. Play colors – red, orange, yellow, blue, green etc |
Opal and Tourmaline are the October birthstones. Opal is a gem of many colors.
This gem of sedimentary silica has grids of silica spheres which show a play of colors created thru
diffraction. The size of the spheres determine the wavelengths and therefore the colors seen. The brilliance of the colors are determined by the regularity of the grid. These changing colors of opal has been used by litterateurs down the ages, from Shakespeare onwards, to symbolize a shifting mind and unsteadiness. There is a superstition that suggests that it is bad luck to wear an opal if opal is not your birthstone. Opals can deteriorate and change from a highly colorful, somewhat glassy stone to a rather colorless mass of a chalky silicon dioxide. That is because opals are unstable and are just one of the phases through which gel-like silica(SiO2) can pass on its way to becoming stable crystalline quartz.
Physical and Chemical Properties
Chemical composition
Silicon dioxide, SiO2, the same elements that make up quartz is also the constituent of opal. Opal is famous for its play of color. The play of color is caused by diffraction of light by the ordered arrangement of closely packed microscopic silica spheres with water enriched spaces between them. The spheres are arranged in octahedrons (base to base pyramids). When the packing of the silica spheres becomes faulted, the striations produce colors that can be seen in reflected light. Play of color is sometimes erroneously called “fire.” The term “fire opal” should be used to describe opals with a red body color; they may or may not show play of colors. Opal is neither very hard (5 1/2 to 6 1/2 on a scale of 10) nor very tough. It has a conchoidal to splintery fracture and is often very brittle.
Colors
The play of colors from the stone can occupy almost any wavelength in the visible spectrum but red and orange are more often preferred than yellow, blue or green. The body color of the opal may be white or tan or bluish. The finest opals have an even distribution of colors in fairly large splotches; pinpoints of light are less desirable. Gray or brown undertones detract from the stone. Some rare opals may show chatoyancy and produce a very fine eye and such stones are desirable even where play of color is insignificant. Opals are fundamentally colorless; various impurities add color to the stone, such as yellow and red from iron oxide and black from manganese oxide and organic carbon. Their milky appearance comes from gas-filled bubbles inside the tiny spherical network. Iridescent opals may also appear to be gray, green, blue, and orange due to the diffraction of light.
Healing Properties and Interesting Information
Healing
Opal Clears, maintains and stimulates each chakra of the body. Attracts inspiration and diminishes fear. Balances the male/female energies in the body, as well as the mind and chakras. A ‘teller’ stone providing insight to shamen. This October birthstone is believed to be beneficial to eyesight.
Where Found
Old World sources for opal were Czechoslovakia and Hungary. Many important opal fields were discovered in New South Wales, South Australia, and Queensland in Australia in the late 19th Century. These fields still produce much of the world’s opal but newer sources have been discovered in Brazil, Guatemala, Honduras, and Mexico. In the United States, opal has been found and commercially worked in Nevada, Oregon and Idaho. The finest opals come from Australia, but are also found in Japan, Mexico, Guatemala, Honduras, India, New Zealand, Iceland, and the western United States (Nevada, Idaho, and California). Black opals, the most rare and valuable, are found only in Australia and Indonesia.
History, mythology
For the ancient Romans, opals symbolized hope and good luck. During early Medieval times,people even wore opals to maintain a strong heart, prevent fainting, protect against infection, and cleanse foul-smelling air.
Buying and Caring tips
Tips for Buying Opal Jewelry
Prices for white opal range between $5 and $100 per carat for a one-carat stone. Black opal have a more specialized market because they are more of a rarity. These October birthstones are highly prized, with prices that range from $250 to $5,000 per carat. Solid opals are the most highly preferred stones but the play of color often is confined to thin layers of horizontally banded opal. Stones called doublets (a thin opal/clear quartz layer) or triplets (a colored back/opal/clear quartz layer) account for many of the opals we see today. Since opals are not very tough, it is best that ring stones or stones that will be making contact with solid objects be doublets or triplets. Some synthetic opal is available as both rough and cut stones and some laboratory made glass products have been fairly good opal substitutes.
Tips to take care of Opal Jewelry
Use a soft dry or damp cloth. Do not soak. Do not use mechanical cleaners. Avoid impacts, dry conditions, heat and chemicals. Opal is a soft gem and is easily prone to getting scratched when rubbed against harder substances. While storing , make sure it is kept in a separate enclosure. If it is set in sterling silver, do not use silver polish for cleaning the jewelry.