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Opals too thin to produce a "natural" opal may be combined with other materials to form "composite" gems. An opal doublet consists of a relatively thin layer of precious opal, backed by a layer of dark-colored material, most commonly ironstone, dark or black common opal (potch), onyx, or obsidian. The darker backing emphasizes the play of color ...
The Koroit opal field is known for the very distinctive type of boulder opal that is found in its mines. In Queensland boulder opal is found within a 300 km wide belt of sedimentary rocks in the Winton Formation. Here opal is found as a kernel in small concretions. [1] The Koroit Opal field was discovered in 1897 by Lawrence Rostron.
Meet the "Virgin Rainbow" – perhaps the finest and certainly the most expensive opal on record. It literally glows in the dark. In fact, as it gets darker around the opal, the opal appears ...
The Fire of Australia opal is a 998 gram uncut opal mined by Walter Bartram in 1946 at the Eight Mile field in Coober Pedy, South Australia. [1] [2] The opal is just under 5,000 carats; roughly equivalent in size to two cricket balls. [1] Although rough-cut, it is polished on two sides. [3]
The Galaxy Opal is the world's largest polished opal, certified by the Guinness Book of World Records in 1992. [1] It was found at the Boi Morto Mine in Brazil in 1976. [ 2 ] The finished opal weighs approximately 3,749 carats , or 0.75 kg.
Biogenic silica (bSi), also referred to as opal, biogenic opal, or amorphous opaline silica, forms one of the most widespread biogenic minerals. For example, microscopic particles of silica called phytoliths can be found in grasses and other plants. Silica is an amorphous metalloid oxide formed by complex inorganic polymerization processes.
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