Types of Opal With Photos
Source: http://www.geologyin.com/2016/06/types-of-opal-with-photos.html Opal is a hydrated amorphous form of silica (SiO2·nH2O), Because of its amorphous character, it is classed as a mineraloid, unlike crystalline forms of silica, which are classed as minerals. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl, […]
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