Why do porphyroblasts form?
Why do porphyroblasts form?
A large crystal that is surrounded by a finer-grained matrix in a metamorphic rock. Porphyroblasts form by the recrystallization of existing mineral crystals during metamorphism. They are analogous to phenocrysts in igneous rock.
How is chlorite formed?
Chlorite forms by the alteration of mafic minerals such as pyroxenes, amphiboles, biotite, staurolite, cordierite, garnet, and chloritoid. Chlorite can also occur as a result of hydrothermal alteration of any rock type, where recrystallization of clay minerals or alteration of mafic minerals produce chlorite.
What minerals make up schist?
Most schists are composed largely of platy minerals such as muscovite, chlorite, talc, sericite, biotite, and graphite; feldspar and quartz are much less abundant in schist than in gneiss.
How is garnet mica schist formed?
Schist is a foliated metamorphic rock made up of plate-shaped mineral grains that are large enough to see with an unaided eye. To become schist, a shale must be metamorphosed in steps through slate and then through phyllite. If the schist is metamorphosed further, it might become a granular rock known as gneiss.
How is a Metaconglomerate rock formed?
Metaconglomerate is formed when conglomerate is subjected to metamorphism. It is easily identifiable by its pebbly and cobbly clasts set in a matrix of sand, silt or clay.
What minerals are in quartzite?
Quartzite: A granoblastic metamorphic rock consisting mainly of quartz (>90%) and formed by recrystallization of sandstone or chert by either regional or thermal metamorphism. Accessory minerals include feldspar, micas, and detrital heavy minerals such as titanite, magnetite, zircon and rutile.
What type of mineral is chlorite is?
silicate minerals
Chlorite is the name of a group of common sheet silicate minerals that form during the early stages of metamorphism. Most chlorite minerals are green in color, have a foliated appearance, perfect cleavage, and an oily to soapy feel. They are found in igneous, metamorphic and sedimentary rocks.
What minerals are in the chlorite group?
The chlorites are a group of phyllosilicate minerals. Chlorites can be described by the following four endmembers based on their chemistry via substitution of the following four elements in the silicate lattice; Mg, Fe, Ni, and Mn. In addition, zinc, lithium, and calcium species are known.
