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The following is a list of rock types recognized by geologists.There is no agreed number of specific types of rock. Any unique combination of chemical composition, mineralogy, grain size, texture, or other distinguishing characteristics can describe a rock type.
[1] [2] Rock that contains greater than 75% ash is considered tuff, while rock containing 25% to 75% ash is described as tuffaceous (for example, tuffaceous sandstone). [3] A pyroclastic rock containing 25–75% volcanic bombs and/or volcanic blocks is called tuff breccia. [4] Tuff composed of sandy volcanic material can be referred to as ...
Andesite is the extrusive equivalent of plutonic diorite. Characteristic of subduction zones, andesite represents the dominant rock type in island arcs. The average composition of the continental crust is andesitic. [3] Along with basalts, andesites are a component of the Martian crust.
Diorite is an intrusive igneous rock composed principally of the silicate minerals plagioclase feldspar (typically andesine), biotite, hornblende, and sometimes pyroxene.The chemical composition of diorite is intermediate, between that of mafic gabbro and felsic granite.
Andesine occurs in intermediate igneous rocks such as diorite, syenite, and andesite. It characteristically occurs in metamorphic rocks of granulite to amphibolite facies commonly exhibiting antiperthite texture. It also occurs as detrital grains in sedimentary rocks.
The significance of porphyritic texture as an indication that magma forms through different stages of cooling was first recognized by the Canadian geologist, Norman L. Bowen, in 1928. [ 8 ] Porphyritic texture is particularly common in andesite , with the most prominent phenocrysts typically composed of plagioclase feldspar .
Trachyandesite is an extrusive igneous rock with a composition between trachyte and andesite. It has little or no free quartz , but is dominated by sodic plagioclase and alkali feldspar . It is formed from the cooling of lava enriched in alkali metals and with an intermediate content of silica .
The individual crystals in an aphanitic igneous rock are not distinguishable to the naked eye. Examples of aphanitic igneous rock include basalt, andesite, and rhyolite. Glassy or vitreous textures occur during some volcanic eruptions when the lava is quenched so rapidly that crystallization cannot occur. The result is a natural amorphous glass ...