变质岩形成时岩石(沉积岩、火成岩或以前的变质岩)在高压力和/或温度。压力和温度力的原子形成新矿物,从而一种新的岩石。它不是必要的支离破碎,但岩石,而变形通过*再结晶*到一个新的国家在应对压力和温度的材料重新组织。(再结晶)[1]不删除任何材料,它仅仅是一个物理重组紧凑的岩石。如果发生一些化学成分的变化,这叫做“交代”。(交代)[2]原子从岩石的一部分,通常与水有关。一个好的岩石学家通常可以确定什么样的母岩,*原岩*,已经变质,到什么程度,但有时很难做识别的区别如风化板岩和页岩甚至花岗岩和片麻岩。然而,形成岩石的过程是不同的,仔细看看矿物质是可能理解什么样的过程,形成了岩石。程度的变质作用称为变质*相*。[![Metamorphic phases][3]][3] *1, Blueschist facies 2, Eclogite facies 3, Prehnite-pumpellyite-facies 4, Greenschist facies 5, Amphibolite-facies 6, Granulite facies 7, Zeolite facies 8, Albite-epidote-hornfels facies 9, Hornblende-hornfels facies 10, Pyroxene-hornfels facies 11, Sanidinite facies* So for example, if a rock has been exposed to very high pressure, but only a few hundred degrees, a Blueschist is formed, whiles hornfels are formed at $400-800^oC$ but low pressure. Igneous rocks are formed when a melt hardens to crystals and sedimentary rocks are formed from sediments. At lower degrees of metamorphism, features of the original rock is preserved. E.g. you can see ripples and even fossils in slates or deformed structures from the source rock, but at higher degrees of metamorpism it's increasingly difficult to imagine how the parent material looked like. Gneiss formed from sandstone and granite can look very similar as the lihology represents the conditions of metamorphism, not the protolith. All rocks weather if exposed to water and air, and weathered material is transported by rivers to oceans where sandstone can be formed from the sand at the beach and shale from the finer sediments further away from the coast. Igneous rocks can be formed as hot magma intrudes the crust and slowly cools down and minerals are formed or form lava at volcanoes. You can read more about the rock cycle e.g. [here][4] to learn more about rock types and how they are formed from each other. [1]: https://en.wikipedia.org/wiki/Recrystallization_(geology) [2]: https://en.wikipedia.org/wiki/Metasomatism [3]: https://i.stack.imgur.com/wcisW.png [4]: http://www.cotf.edu/ete/modules/msese/earthsysflr/rock.html