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Ijolite – Igneous rock consisting essentially of nepheline and augite; Jadeitite – Metamorphic rock found in blueschist-grade metamorphic terranes; Jasperoid – A hematite-silica metasomatite analogous to a skarn; Kenyte – Type of igneous rock - A variety of phonolite, first found on Mount Kenya
Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock ( protolith ) is subjected to temperatures greater than 150 to 200 °C (300 to 400 °F) and, often, elevated pressure of 100 megapascals (1,000 bar ) or more, causing profound physical or chemical changes.
Igneous rock (igneous from Latin igneus 'fiery'), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial melts of existing rocks in either a planet's mantle or crust.
These rocks are fine-grained and sometimes cool so rapidly that no crystals can form and result in a natural glass, such as obsidian, however the most common fine-grained rock would be known as basalt. Any of the three main types of rocks (igneous, sedimentary, and metamorphic rocks) can melt into magma and cool into igneous rocks. [2]
A fine-grained, mafic igneous rock composed predominantly of ferromagnesian minerals and with lesser amounts of calcium-rich plagioclase feldspar. basement rock The thick foundation of ancient, and oldest metamorphic and igneous rock that forms the crust of continents, often in the form of granite. basic rock Igneous rock with low silica ...
Persuaded by the close connection between migmatization and granites in outcrop, Sederholm considered migmatites to be an intermediary between igneous and metamorphic rocks. [20] [21] He thought that the granitic partings in banded gneisses originated through the agency of either melt or a nebulous fluid, the ichor, both derived from nearby ...
Gneiss (/ n aɪ s / nice) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. This rock is formed under pressures ranging from 2 to 15 kbar, sometimes even more, and temperatures over 300 °C (572 °F).
In igneous and metamorphic rocks, grain size is a measure of the sizes of the crystals in the rock. In igneous rock, this is used to determine the rate at which the material cooled: large crystals typically indicate intrusive igneous rock, while small crystals indicate that the rock was extrusive. [17]