{"id":352,"date":"2015-09-14T18:35:45","date_gmt":"2015-09-14T18:35:45","guid":{"rendered":"https:\/\/courses.candelalearning.com\/geophysical\/?post_type=chapter&p=352"},"modified":"2017-04-19T21:55:03","modified_gmt":"2017-04-19T21:55:03","slug":"metamorphic-rock","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-geophysical\/chapter\/metamorphic-rock\/","title":{"raw":"Metamorphic Rock","rendered":"Metamorphic Rock"},"content":{"raw":"\"Picture\"<\/a>\r\n
\r\n\r\nMetamorphism<\/strong> is the addition of heat and\/or pressure to existing rocks, which causes them to change physically and\/or chemically so that they become a new rock. Metamorphic rocks may change so much that they may not resemble the original rock. Any type of rock\u2014igneous, sedimentary, or metamorphic\u2014can become a metamorphic rock. All that is needed is enough heat and\/or pressure to alter the existing rock\u2019s physical or chemical makeup without melting the rock entirely. Rocks change during metamorphism because the minerals need to be stable under the new temperature and pressure conditions. The need for stability may cause the structure of minerals to rearrange and form new minerals. Ions may move between minerals to create minerals of different chemical composition. Hornfels, with its alternating bands of dark and light crystals, is a good example of how minerals rearrange themselves during metamorphism.\r\n\r\nExtreme pressure may also lead to foliation, the flat layers that form in rocks as the rocks are squeezed by pressure. Foliation normally forms when pressure is exerted in only one direction. Metamorphic rocks may also be non-foliated. Quartzite and limestone are nonfoliated.\u00a0The two main types of metamorphism are both related to heat within Earth:\r\n