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The original rock (protolith) could be sedimentary, igneous, or existing metamorphic rock which is subjected to heat (temperatures greater than 150 to 200 °C) and pressure (100 megapascals (1,000 bar) or more), causing profound physical or chemical change.
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Petroleum Industry / Upstream / Subsurface E&P Disciplines / Petroleum Geology + Petrophysics / Rock
[ Sedimentary ] [ Igneous ] [ Metamorphic rock ]