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The other minerals in the rock are termed accessory minerals, and do not greatly affect the bulk composition of the rock. Rocks can also be composed entirely of non-mineral material; coal is a sedimentary rock composed primarily of organically derived carbon. [34] [38]
Other common accessory minerals include spinel, garnet, biotite, or magnetite. A peridotite containing significant amounts of one of these minerals may have its classification refined accordingly; for example, if a lhertzolite contains up to 5% spinel, it is a spinel-bearing lhertzolite , while for amounts up to 50%, it would be classified as a ...
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 ...
Harzburgite, an ultramafic, igneous rock, is a variety of peridotite consisting mostly of the two minerals olivine and low-calcium (Ca) pyroxene ; it is named for occurrences in the Harz Mountains of Germany. It commonly contains a few percent chromium-rich spinel as an accessory mineral.
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Rutile is a common accessory mineral in high-temperature and high-pressure metamorphic rocks and in igneous rocks. Thermodynamically, rutile is the most stable polymorph of TiO 2 at all temperatures, exhibiting lower total free energy than metastable phases of anatase or brookite. [7]
Common mafic accessory minerals are amphibole, biotite or pyroxene. Small amounts of nepheline may be present and apatite is a common accessory mineral. [2] Trachyandesite is not a recognized rock type in the QAPF classification, which is based on the actual mineral content. However, latite is recognized in this classification, while benmoreite ...
Trondhjemite is an orthoclase-deficient variety of sodium-rich tonalite with minor biotite as the only mafic mineral, named after Norway's third largest city, Trondheim. [7] Tonalites, together with granodiorites, are characteristic of calc-alkaline batholiths formed above subduction zones. [8]