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Grain size in igneous rocks results from cooling time so porphyritic rocks are created when the magma has two distinct phases of cooling. [18] Igneous rocks are classified on the basis of texture and composition. Texture refers to the size, shape, and arrangement of the mineral grains or crystals of which the rock is composed. [citation needed]
Silicic is an adjective to describe magma or igneous rock rich in silica. The amount of silica that constitutes a silicic rock is usually defined as at least 63 percent. [ 1 ] Granite and rhyolite are the most common silicic rocks .
Also called Indianite. A mineral from the lime-rich end of the plagioclase group of minerals. Anorthites are usually silicates of calcium and aluminium occurring in some basic igneous rocks, typically those produced by the contact metamorphism of impure calcareous sediments. anticline An arched fold in which the layers usually dip away from the fold axis. Contrast syncline. aphanic Having the ...
In geology, a facies (/ ˈ f eɪ ʃ ɪ. iː z / FAY-shih-eez, US also / ˈ f eɪ ʃ iː z / FAY-sheez; same pronunciation and spelling in the plural) [a] is a body of rock with distinctive characteristics. [1]
Leucitite – igneous rock most common in lavas of recent and Tertiary age, which have a fair amount of potassium Lherzolite – an ultramafic and ultrabasic rock that is composed of olivine and pyroxene Pages displaying wikidata descriptions as a fallback – An ultramafic rock, essentially a peridotite
Granite (/ ˈ ɡ r æ n ɪ t / GRAN-it) is a coarse-grained intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies underground. It is common in the continental crust of Earth, where it is found in igneous ...
Rhyolite is an extrusive igneous rock, formed from magma rich in silica that is extruded from a volcanic vent to cool quickly on the surface rather than slowly in the subsurface. It is generally light in color due to its low content of mafic minerals, and it is typically very fine-grained ( aphanitic ) or glassy .
Chart illustrating the meaning of peralkaline, metaluminous, peraluminous and subaluminous. Metaluminous rocks are igneous rocks that have a molar proportion of aluminium oxide lower than the combination of calcium oxide, sodium oxide and potassium oxide. [1]