Metamorphic rocks

• Metamorphic rocks started out as some other type of rock, but have been substantially changed from their original igneous, sedimentary, or earlier metamorphic form.
• Rocks that undergo a change to form a new rock are referred to as metamorphic rocks.
• The process by which a rock is transformed from one rock type into another is called Metamorphism.
• Temperature plays a crucial role in metamorphism, as it increases, mineral reactions and recrystallization become more likely.
• The rock is generally very hard, strong, dense and uniformly grained.
• The rock finds extensive use in building and road construction.
• Marble is a granular metamorphic rock composed chiefly of recrystallized limestone.
• Marble is commonly used in the construction of palatial and monumental buildings in the form of blocks, slabs, arches and in the crushed form as chips for flooring.
• The Scottish Highlands, UK, is a location for metamorphic landforms.
• The Southern Alps, New Zealand, is a location for metamorphic landforms.
• Lofoten Islands, Norway, is a location for metamorphic landforms.
• The Drakensberg Mountains, South Africa, is a location for metamorphic landforms.
• The Himalayas, Asia, is a location for metamorphic landforms.
• Different minerals have specific temperature ranges within which they are stable, and elevated temperatures facilitate the growth of new minerals and the rearrangement of existing ones.
• The source of heat in metamorphism can be magmatic intrusions, deep burial, or tectonic forces.
• Pressure, or the force applied to rocks, affects the density and arrangement of minerals, with higher pressures typically associated with depth in the Earth’s crust.
• The presence of chemically active fluids, typically groundwater or hydrothermal solutions, can enhance metamorphism, promoting mineral reactions, altering mineral compositions, and facilitating the exchange of elements.
• Gneissose Structure: If the rock consists of equidimensional minerals along with other first segregation of the minerals occur and alternating bands are formed, then foliation and lineation of platy and prismatic minerals take place.
• Gneiss: A texture or arrangement of minerals is called gneissose structure.
• Schistose Structure: If the rock consists of only prismatic or platy minerals, then no segregation takes place but only foliation and/or lineation.
• Granular Structure: If the rock is composed predominantly of equidimensional minerals, then neither segregation nor foliation takes place.
• Quartzite: As the name indicates, it is produced under the influence of direct pressure in the upper zones of earth's crust.
• Cataclastic Structure: In some rocks more resistant minerals may remain unaffected, while the softer minerals are powdered to fine material.
• Porphyroclastic Structure: This result in an appearance similar to porphyritic texture and is called porphyroclastic structure.
• Intermediate-Grade Metamorphic Rocks: Metamorphic rocks can be classified based on the degree of metamorphism they have undergone.
• Low-Grade Metamorphic Rocks: Metamorphic rocks can also be classified based on the degree of metamorphism they have undergone.
• Ultrahigh-Grade Metamorphic Rocks: Metamorphic rocks can also be classified based on the degree of metamorphism they have undergone.
• Quartzo-Feldspathic: Rocks that originally contained mostly quartz and feldspar like granitic rocks and arkosic sandstones will also contain an abundance of quartz and feldspar as metamorphic rocks, since these minerals are stable over a wide range of temperature and pressure.
• Calcareous: Calcareous rocks are calcium rich.
• The composition and mineral content of the original rock, known as the protolith, strongly influence the type of metamorphism that will occur, with different minerals having distinct stability ranges.
• The duration of exposure to metamorphic conditions is another critical factor, slow, long-term metamorphism allows for more extensive mineral changes and recrystallization, while rapid metamorphism may result in less pronounced alterations.
• Tectonic forces, resulting from the movement of Earth’s tectonic plates, can exert pressure and create stress on rocks, leading to regional metamorphism.
• Rocks with pre-existing foliation or alignment of minerals are more likely to develop foliated textures during metamorphism.
• The composition of the fluids that come into contact with the rock can impact metamorphism.
• Basic metamorphic rocks are generally derivatives of basic igneous rocks like basalts and gabbros.
• Basic metamorphic rocks contain an abundance of Fe-Mg minerals like biotite, chlorite, and hornblende, as well as calcic minerals like plagioclase and epidote.
• Magnesian Rocks are rich in Mg with relatively less Fe, and contain Mg-rich minerals like serpentine, brucite, talc, dolomite, and tremolite.
• In general, such rocks usually have an ultrabasic protolith, like peridotite, dunite, or pyroxenite.
• Ferriginous Rocks are rich in Fe with little Mg and are characterized by an abundance of Fe-rich minerals like greenalite, ferroactinolite, hematite, and magnetite at low grades, and ferrosilite, fayalite, ferrohedenbergite, and almandine garnet at higher grades.
• Manganiferrous Rocks are characterized by the presence of Mn-rich minerals and are characterized by such minerals as Stilpnomelane and spessartine.