- A fine-grained
igneous rock with no
composted of about 75 percent plagioclase
balance ferromagnesian silicates.
Important as lavas; possibly derived by fractional
basaltic magma. Widely
characteristic of mountain-making processes around
borders of Pacific Ocean. Confined to continental sectors.
Source: Leet, L. Don. 1982.
Physical Geology, 6th Edition. Englewood Cliffs, NJ: Prentice-Hall
- A dark-colored, fine-grained extrusive rock that, when porphyritic,
contains phenocrysts composed primarily of zoned sodic plagioclase (esp.
andesine) and one or more of the mafic minerals (e.g., biotite,
hornblende, pyroxene), with a groundmass composed generally of the same
minerals as the phenocrysts, although the plagioclase may be more sodic,
and quartz is generally present; the extrusive equivalent of diorite.
Andesite grades into latite with increasing alkali feldspar content, and
into dacite with more alkali feldspar and quartz. It was named by Buch in
1826 from the Andes Mountains, South America. AGI
Dictionary of Mining, Mineral, and Related Terms