andesite -- Igneous volcanic rock, less mafic than basalt, but more mafic than dacite; rough volcanic equivalent of diorite.
anticline -- A fold of rock layers that is convex upwards. Antonym of syncline.
andesite line The geographic boundary between rocks of the Pacific Basin, which are basaltic, and those around the rim of the basin, which are in part andesitic.
angle of incidence The angle at which a ray of energy approaches a surface.
Andesite
An extrusive igneous rock that develops from a magma that is chemically between felsic and mafic and whose mineral crystals are fine.
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The andesite line is the most significant regional distinction in the Pacific. It separates the deeper, mafic igneous rock of the Central Pacific Basin from the partially submerged continental areas of felsic igneous rock on its margins.
The occurrence of andesites leads to several postulates: 1) these rocks are evidence of some differentiation in the martian mantle; 2) they may represent rocks involved in subcrustal release of water; or 3) they are anomalous local thin veneers on ...
 See also: Area, Volcanic, Surface, Region, Basalt
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