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Opal Foundation
Opal is a hydrated amorphous form of silicon dioxide, silica (SiO2·''n''H2O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Due to its amorphous property, it is classified as a mineraloid, unlike crystalline forms of silica, which are considered minerals. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock (geology), rock, being most commonly found with limonite, sandstone, rhyolite, marl, and basalt. The name ''opal'' is believed to be derived from the Sanskrit word (), which means 'jewel', and later the Greek derivative (), which means 'to see a change in color'. There are two broad classes of opal: precious and common. Precious opal displays play-of-color (iridescence); common opal does not. Play-of-color is defined as "a pseudo chromatic optical effect resulting in flashes of colored light from certain minerals, as they are turned in white light." The internal structure of pr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mineraloid
A mineraloid is a naturally occurring mineral-like substance that does not demonstrate crystallinity. Mineraloids possess chemical compositions that vary beyond the generally accepted ranges for specific minerals. For example, obsidian is an amorphous glass and not a crystal. Jet is derived from decaying wood under extreme pressure. Opal is another mineraloid because of its non-crystalline nature. Pearl is considered a mineraloid because the included calcite and/or aragonite crystals are bonded by an organic material, and there is no definite proportion of the components. Examples * Allophane, solid (IMA/CNMNC valid mineral name) * Amber, non-crystalline structure, organic * Anthracite or hard coal * Bituminous coal * Chlorophaeite * Chrysocolla, solid (IMA/CNMNC valid mineral name) * Deweylite, a mixture of serpentine and talc or stevensite * Diatomite * Ebonite, vulcanized natural or synthetic rubber (organic); lacks a crystalline structure * Fulgurite, a variety of the mine ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
