Rhyodacite
A rock classification type
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About Rhyodacite
Fine grained igneous rocks intermediate between rhyolite and dacite, containing >10% quartz and subequal amounts of plagioclase and alkali feldspar. About 35-65% of feldspars are plagioclase. The extrusive equivalent of granodiorite. The principal minerals, sodic plagioclase, K-feldspar, quartz, and minor 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
Ref: AGI
Unique Identifiers
Mindat ID:
48448
Long-form identifier:
mindat:1:1:48448:4
Classification of Rhyodacite
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 Rhyodacite
- Rhyodacite
Mineralogy of Rhyodacite
Essential minerals - these are minerals that are required within the classification of this rock:
| Feldspar > Alkali Feldspar | A subgroup of the Feldspar Group, poor in calcium, and mostly rich in potassium. |
| Feldspar > Plagioclase | (Na,Ca)[(Si,Al)AlSi2]O8 |
| Silica > Quartz | SiO2 |
Non-essential minerals - these minerals are common, sometimes major components, but are not always present:
| Amphibole > Hornblende | AnCa2(Z2+5-mZ3+m)(Si8-(n+m)Al(n+m))(OH,F,Cl)2 |
| Pyroxene > Clinopyroxene > Augite | (CaxMgyFez)(Mgy1Fez1)Si2O6 |
Synonyms of Rhyodacite
Internet Links for Rhyodacite
mindat.org URL:
https://www.mindat.org/min-48448.html
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Please feel free to link to this page.
References for Rhyodacite
Reference List:
Rio Morteo, Albenga, Savona Province, Liguria, Italy