Metamorphic rock the foliation is called "gneissosity"), granoblastic (includes granulite, some marbles and quartzite), and hornfelsic (includes hornfels and skarn). Metamorphic rock Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means "change in form". The original rock (protolith) is subjected to heat (temperatures greater than 150 to 200 °C) and pressure ( or more), causing profound physical or chemical change. The protolith may be a sedimentary, igneous, or existing metamorphic rock. Metamorphic rocks make up a large part of the Earth's crust and form 12% of the Earth's land surface. They are classified by
Change of variables (PDE) can thus be visualized as rotation on torii. As a particular example, consider the simple harmonic oscillator, with formula_70 and formula_71, with Hamiltonian formula_72. This system can be rewritten as formula_73, formula_74, where formula_75 and formula_76 are the canonical polar coordinates: formula_77 and formula_78. See V. I. Arnold, `Mathematical Methods of Classical Mechanics', for more details. Change of variables (PDE) Often a partial differential equation can be reduced to a simpler form with a known solution by a suitable change of variables. The article discusses change of variable for PDEs below in two ways: For example, the following simplified form