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Andesite

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Name:
It was named by Buch in 1826 from the Andes Mountains, South America.
A dark-colored, fine-grained, mostly extrusive rock that is approximately the fine grained equivalent of diorites. When porphyritic, they contain phenocrysts composed primarily of zoned sodic plagioclase (esp. andesine) and one or more mafic minerals (e.g., biotite, hornblende, pyroxene, usually <20%), with a groundmass composed generally of the same minerals as the phenocrysts, although the plagioclase may be more sodic, and quartz is generally present in small amounts. Andesite grades into latite with increasing alkali feldspar content, and into dacite with more alkali feldspar and quartz. Basalt is similar but with more mafics and minimal quartz and alkali feldspar; basaltic andesite is intermediate.

Andesitic rocks plot on the QAPF diagram with 0-20% quartz, and >65% of feldspars being plagioclase; on the TAS diagram: <57-63% SiO2, (Na2O+K2O)<~6%


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Classification of AndesiteHide

Andesite appears in field 9 and 10 in the QAPF diagram.

Syntax error: Incorrect or missing DIAG type

Sub-divisions of AndesiteHide

Mineralogy of AndesiteHide

Essential minerals - these are minerals that are required within the classification of this rock:
Feldspar > PlagioclaseA petrological term for Albite-Anorthite Series.
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 ...
Mica > BiotiteA series or subgroup of the Mica Group.
PyroxeneA petrological term for Pyroxene Group.

Internet Links for AndesiteHide

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