Opal Gemstone Information
About Opal - History and Introduction
Opal is a gem-quality form of hydrated amorphous silicon dioxide. Its name is derived from the Sanskrit word for 'stone'. It is gemologically classed as a mineraloid rather than a mineral, owing to its amorphous form. Opal is considered to be the national gemstone for Australia, owing to the fact that Australia produces roughly 97% of the world's entire supply of opal gemstones. Opals can be divided into three main subgroups: precious opal, fire opal and common opal (potch).
Opal is famed for its ability to diffract light. The exact cause of opal's unique properties was only recently discovered by Australian scientists in the 1960s after analysis with electron microscopes. It was discovered that small spheres of silica gel caused interference, refraction and diffraction of light, resulting in opal's distinctive play of color. The varying refractive indices of the spheres and spaces between them dissect the light on its passage through the stone. As light enters the opal, it bends around the tiny particles or 'spheres' of hydrated silica, as well as 'chips' of silicon and oxygen suspended within the stone. Light is comprised of all visible colors and can produce an entire spectrum of colors when it is diffracted.
Precious opal is known for its remarkable ability to diffract light, which results in rainbow-like colors that change with the angle of observation - known as 'play of color'. Fire opal can sometimes exhibit slight color play, but it is better known for its vivid body color. Common opal is usually opaque, rarely translucent, and lacks play of color. It is often found mixed with other gemstones, such as agate opal or moss opal. Common opal is known to exhibit 'opalescence'. The term 'opalescence' is often mistaken for 'play of color'. Opalescence should technically only be used to describe the optical effects seen in common opal. Opalescence is caused by the reflection of light and appears as a sheen of light, typically milky-bluish in color. It is a form of adularescence, whereas 'play of color' is iridescence caused by light diffraction.
Identifying Opal Back to Top
Opal by definition is hydrated silicon dioxide, always containing from three to thirty percent water. This characteristic and its relative softness with a rating of 5.5 to 6.5 makes opal quite easy to identify and distinguish from other gemstones. Unlike other gems with play of color or iridescent effects, opal also exhibits 'opalescence'. Other iridescent stones do not display this pearl-like bluish color effect that appears to glide across opal, but instead, will usually show color that will abruptly appear, disappear and then reappear, depending on the viewing angle. In most cases, close observance of color and optical phenomena can usually help distinguish opal from other similar gemstones.
Opal; Origin and Sources Back to Top
The most important deposits are located in Australia. Around 95 percent of the world's supply of white precious opals are mined "down under". Famous deposits in New South Wales are at Lightning Ridge and White Cliffs, in South Australia at Coober Pedy and Andamooka. Various deposits are also found in Queensland.
Other deposits are found in Brazil, Ethiopia, Guatemala, Honduras, Indonesia, Japan, Mexico, Russia and the United States (Idaho and Nevada).
Buying Opal and Determining Opal Value Back to Top
Opal Gemological Properties: Back to Top
Please refer to our Gemstone Glossary for details of gemology-related terms.
Opal: Related or Similar Gemstones Back to Top
Opal is hydrated silicon dioxide, which means it has an extremely high water content and an amorphous crystal structure. There are many different varieties of opal with some being extremely rare and valuable. In addition, there are also several unofficial 'marketing' names used for opals based on specific localities, inclusions and other properties.
The following lists some of the most well-known opal trade names, with a short description:
Opal Mythology, Metaphysical and Crystal Healing Back to Top
The name opal was probably derived from Sanskrit "upala", meaning "valuable stone" or from the Greek word "opallus" which means to see a change in color. Later, the Latin word "opalus" evolved, meaning precious stone. In the days of Roman antiquity there existed a so-called "opalus", or a "stone from several elements". Pliny the Elder, the famous Roman author, called opal a gemstone which combines the best possible characteristics of the most beautiful of gemstones; the fine sparkle of almandine, the shining purple of amethyst, the golden yellow of topaz, and the deep blue of sapphire, "so that all colors shine and sparkle together in a beautiful combination". According to an old Australian Aboriginal legend, the Creator came down from the heavens on a rainbow and delivered a message of peace for all mankind. Stones that were near the place where His feet touched the ground suddenly came to life and began to sparkle. This was believed to be the birth of opal.
For ages people have believed in the healing power of opal. It is reported to be able to solve depression and to help its wearer find true and real love. Opal is also said to stimulate originality and creativity. Opal is porous and because of this, it is quite absorbent. Due to its ability to absorb, it is thought that it can pick up the thoughts and feelings of people and amplify emotions. Opal is a birthstone for those who are born in October.
Opal Gemstone and Jewelry Design Ideas Back to Top
Opals are best suited for earrings, brooches and pendants. Due to the delicate nature of opals, they are not recommended to be worn daily as rings or other types of jewelry that are subject to hard knocks. Opals can be drilled to make attractive pendants for necklaces or earrings. They can also be bezel set or wire-wrapped for occasional-wear rings, bracelets, necklaces and pendants. Tumbled opals also make eye-catching beads. Opals are also often carved in ornamental designs, such as animal or flower carvings.
Note: Buy colored gemstones by size and not by carat weight. Colored stones vary in size-to-weight ratio. Some stones are larger and others are smaller than diamonds by weight in comparison.
Famous Opal Gemstones Back to Top
'Big Ben' is a white precious opal of over 800 grams, more than 4000 carats, which was found at Lightning Ridge, Australia.
'The Light of the World' is a white precious opal of 40 grams, 2,250 carats, which was found in Australia. It is considered to be the most colorful white opal of all time.
The 'Andamooka Desert Flame', is the largest opal ever brought to the light of day; weighing 6,843 kilograms.
Opal Gemstone Jewelry Care and Cleaning Back to Top
Opals are delicate gemstones. Their most significant weakness has to do with their water content. If an opal is allowed to dry, it will crack and fade. If you live in a very dry climate, or keep them in a dehumidified room, some precautions are necessary. Keeping them in a tight plastic bag, with a damp piece of cotton or fabric will prevent dehydration. Because of their water content, opals are also highly sensitive to sudden changes in temperature.
Being somewhat soft, opals scratch easily. It is important to realize that a large component of ordinary dust is quartz at 7 (Mohs scale) in hardness. At 5.5 to 6 in hardness, simply wiping the dust off an opal will gradually reduce its polish. The solution is to clean your opals using a soft cloth and only mild soap or detergent if needed. Do not use harsh chemical or cleaners and avoid ultrasonic cleaners and steamers. Always remove opal jewelry before engaging in vigorous physical activity.
- First Published: December-15-2006
- Last Updated: March-07-2014
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