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[5] [6] A granite containing both muscovite and biotite micas is called a binary or two-mica granite. Two-mica granites are typically high in potassium and low in plagioclase, and are usually S-type granites or A-type granites, as described below. [7] [8] Another aspect of granite classification is the ratios of metals that potentially form ...
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.
The granitoid rocks are mainly potassic granite and were derived principally from reworked older (3.1–2.8 Ga) gneiss. [3] During the Paleoproterozoic, island-arc terrane associated with the Colorado orogeny accreted to the Wyoming Craton along the Cheyenne belt, a 500-km-wide belt of Proterozoic rocks named for Cheyenne, Wyoming.
Granite rock hand-sized sample. A granitoid is a generic term for a diverse category of coarse-grained igneous rocks that consist predominantly of quartz, plagioclase, and alkali feldspar. [1] Granitoids range from plagioclase-rich tonalites to alkali-rich syenites and from quartz-poor monzonites to quartz-rich quartzolites. [2]
It characterizes one of the most well-preserved and oldest pieces of continental crust today by containing rocks in the Barberton Granite Greenstone Terrain (3.55–3.22 Ga). The BGB is a small, cusp-shaped succession of volcanic and sedimentary rocks, surrounded on all sides by granitoid plutons which range in age from >3547 to <3225 Ma. [1]
A-type granite is a particular category of the S-I-A-M or 'alphabet' system which classifies granitoids and granitic rock by their photoliths or source. [1] [2] The 'A' stands for Anorogenic or Anhydrous, as these granites are characterized by low water content and a lack of orogenic or transitional tectonic fabric. [3]
Igneous rocks are divided into two main categories: Plutonic or intrusive rocks result when magma cools and crystallizes slowly within the Earth's crust. A common example of this type is granite. Volcanic or extrusive rocks result from magma reaching the surface either as lava or fragmental ejecta, forming minerals such as pumice or basalt. [5]
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 ...