There are different types of Opal found worldwide - Black, Fire, White, Pink, Australian Opal and others. In /home/mindat/gemdat/gshow. Opal (Dudhiya Pathar) is a stone widely recognized for its wonderful play of colors. Warning: file_get_contents(): failed to open stream: HTTP request failed! HTTP/1.1 403 Forbidden White opals are the least valuable variety due to the fact that they are the most common variety of opal. Black is considered the most valuable as it enhances and accentuates the play of color (opalescence). Green opal is rare, black opal is known, and the cloudy varieties of milk opal are white. Red, orange and yellow are the most desired spectral colour to be seen in opal and therefore command higher prices. Opals vary widely in body color, with white the most common. In the Middle Ages, opals were considered a good luck talisman as they contained all the virtues of each gemstone combined, including their colour spectrum. In colour these varieties are usually brown, yellow, or red, of various shades. In a pure condition the mineral is perfectly colourless, the tint of the coloured varieties is due to the presence of impurities. Both common and precious varieties of opal are, as a rule, cloudy, being at the best only translucent or semi-transparent. The lustre of natural specimens is only moderately strong, it is increased by cutting and polishing, but even then is in no way remarkable. Opal is a hydrated amorphous form of silica (SiO 2 ·nH 2 O) its water content may range from 3 to 21 by weight, but is usually between 6 and 10. The lustre is usually of the common vitreous type, though in some opals it may be greasy, resinous, or waxy. Precious Opal is conspicuous amongst all others for the magnificent play of colours produced by the refraction and reflection of light in its colourless substance. Their physical properties vary considerably. The best-quality opals have a bright red color with no impurities or. Opal is divided into three subgroups: Precious Opal, yellow-red Fire Opal, and Common Opal. The value of red opals depends on the intensity of their color and their clarity. The amount of water varies in different specimens. The name is derived from an Indian (Sanskrit) word for "stone". There are plenty of shades of blue, which all contain their own unique color attributes.
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