"Andesite is an extrusive igneous, volcanic rock, of intermediate
composition, with aphanitic to porphyritic texture. In a general sense,
it is the intermediate type between basalt and dacite. The mineral
assemblage is typically dominated by plagioclase plus pyroxene and/or
hornblende. Magnetite, zircon, apatite, ilmenite, biotite, and garnet
are common accessory minerals.[1] Alkali feldspar may be present in
minor amounts. The quartz-feldspar abundances in andesite and other
volcanic rocks are illustrated in QAPF diagrams. Relative alkali and
silica contents are illustrated in TAS diagrams.
Classification of andesites may be refined according to the most
abundant phenocryst. Example: hornblende-phyric andesite, if hornblende
is the principal accessory mineral.
Andesite can be considered as the extrusive equivalent of plutonic
diorite. Andesites are characteristic of subduction zones, such as the
western margin of South America. The name andesite is derived from the
Andes mountain range."
I was looking at the Hindu and Buddhist statuary collection (from South
and Souheast Asia) at the Art Institute in Chicago today, and I noticed
that a great many of them were labeled as being made of andesite.
(Others included sandstone and terracota.) Interesting.
Read more:
http://en.wikipedia.org/wiki/Andesite
http://www.newworldencyclopedia.org/entry/Andesite
http://geology.com/rocks/andesite.shtml
http://geology.csupomona.edu/alert/igneous/andesite.htm
"I just wanted you to know"
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