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Rhyodacite

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Rocks intermediate between rhyolite and dacite, containing >10% quartz and subequal amounts of plagioclase and alkali feldspar. The extrusive equivalent of granodiorite. The principal minerals, sodic plagioclase, K-feldspar, quartz, and biotite or hornblende, commonly occur as phenocrysts in a finely crystalline groundmass of feldspar and quartz. Accessory minerals are apatite and magnetite, and occasionally augite.

Ref: AGI


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Classification of RhyodaciteHide

Rhyodacite appears in fields 3 and 4 in the QAPF diagram.

Rhyolitic rocks are found in field 'R' in the TAS diagram.

Sub-divisions of RhyodaciteHide

Mineralogy of RhyodaciteHide

Essential minerals - these are minerals that are required within the classification of this rock:
Feldspar > Alkali FeldsparFeldspar Group minerals rich in Potassium or Sodium.
Feldspar > PlagioclaseA petrological term for Albite-Anorthite Series.
Silica > QuartzSiO2
Non-essential minerals - these minerals are common, sometimes major components, but are not always present:
Amphibole > HornblendeAn informal name for dark green to black amphiboles, mostly ferro-hornblende or ...
Pyroxene > Clinopyroxene > Augite(CaxMgyFez)(Mgy1Fez1)Si2O6

Synonyms of RhyodaciteHide

Internet Links for RhyodaciteHide

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