Category : Minerals

The Black Opal is a hydrated amorphous form of silica (SiO2┬ĚnH2O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. 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 ..

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