This stone has indeed captured the imagination of humankind because of its spectacular variety of color and luminescence. This is one of the only gemstones that have relatively high water content, and a structure much like that of quartz. Opal is a soft stone and, though prone to breakage, has been immensely popular through the ages. This gemstone is mined throughout the Western United States, Australia and western Africa. Wearing opal next to the skin is thought to improve its wear ability since it absorbs moisture and oils from the skin.
History
This stone has a long history dating thousands of years to the ancient Romans but did not have a great impact in modern times until the late nineteenth century. The early twentieth century saw the rise of the art deco movement and opals gained tremendous notoriety. Easily carved and shaped, this stone was favored as a medium for sculpted jewelry and was often used in the creation of cameo pieces with white on black the predominant combination of color relief. The use of opal continued into the period known as retro. Both art movements stressed flowing lines and smooth curves and carving opal lent itself well to these periods. Thought to be a desert stone, opal of extraordinary color combinations are found in Australia and have the stone have long been held in high regard by the aboriginal peoples of the Australian outback.
Birthstone Information
Topaz is recognized as the birthstone for October and is associated with the astrological birth sign of Cancer. People born under the sign of Aries are thought to increase their luck by wearing a black opal.
New Age Beliefs and Powers Through The Ages
A belief has persisted throughout modern history that this stone could bring bad luck to the bearer. In contrast, the ancient Greeks and Romans ascribed great powers to opal with the Greeks believing that this stone could impart the powers of prophesy and great insight. In Asia and the Middle East, this stone was thought to be a gift from the heavens. In modern times it was thought that bad luck could befall those who wore opal or received it as a gift. This belief was thought to be especially true if the wearer was not born under the astrological sign of Aries or not born in the month of October.
Artificial Forms of Enhancement
There are several techniques used to artificially enhance the color and appearance of naturally-occurring opal stones. In order to fill in cracks and other surface imperfections the stones are often oiled or coated with wax or plastic. In order to produce black stones, smoking is often employed as well as the use of chemical dyes since the stone is prone to absorb liquid and retain the color.
General Scientific Information
The chemical name SiO2 . nH2O. An opal can contain six percent to ten percent water and can range as high as twenty percent.
Hardness measures 5.5 to 6.5 on the Mohs scale - the Mohs scale measures the hardness of metals, minerals, gemstones and crystals on a scale of 1 to 10. For example the hardness properties of most quartz crystals fall around 7 on the scale, as does steel and titanium. Diamond is the hardest known substance on the Mohs scale coming in at a hard 10. To most consumers hardness generally reflects the stones able to resist scratches and cracks.
There is no cleavage found in opal.
The index of refraction ranges between 1.44 and 1.47 and generally indicates the purity of the stone.
The specific gravity is 1.99 - 2.25.
The crystalline system is amorphous.
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