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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.
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.
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The rocks are 70 percent plutons and 30 percent supracrustal formed between 1.765 and 1.4 billion years ago in the Proterozoic, based on uranium-lead dating. All of the rocks more than 1.65 billion years old show evidence of metamorphism ranging between greenschist and amphibolite grade on the sequence of metamorphic facies.
[33] [34] Subsequent erosion of the mountains exposes the roots of the orogenic belt as extensive outcrops of metamorphic rock, [35] characteristic of mountain chains. [33] Metamorphic rock formed in these settings tends to shown well-developed foliation. [33] Foliation develops when a rock is being shortened along one axis during metamorphism.
The oldest Proterozoic metamorphic and igneous rocks were intruded with granites and pegmatite between 1.45 and 1.4 billion years ago. The Oracle Granite, near Tucson, the Ruin Granite, close to the Ray-Superior area, and the Zoroaster Granite at the base of the Grand Canyon all contain one to two inch long, pink orthoclase crystals.
This is a list of minerals which have Wikipedia articles. Minerals are distinguished by various chemical and physical properties. Differences in chemical composition and crystal structure distinguish the various species .
On a map showing only metamorphic rocks, the Canadian Shield forms a circular pattern north of the Great Lakes around Hudson Bay.. The Canadian Shield is a large area of Archean through Proterozoic igneous and metamorphic rocks in eastern Canada and north central and northeastern United States.