Diatomite - PetroWiki


Diatomite The term'Diatomite' is used to refer to biogenic, siliceous deposits composed mainly of the frustules of diatoms with varying amounts of detrital material, mainly clay & silt. The diatoms, which are pelagic phyto-plankton, are composed of amorphous colloidal silica, in the so-called Opal A phase of silica mineralogy. The diatoms sink to the bottom of the ocean or lake to form an ooze that gradually becomes lithified as the water is squeezed out. At about 125ºF, due to increasing depth of burial, the Opal A becomes unstable and changes diagenetically into Opal CT. (Opal CT is sometimes called'porcelanite' because it has a porcelain-like texture.) Dissolution and recrystallization of the Opal A results in the minerals cristobalite & tridymite, which are more stable forms of silica.

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