Igneous, sedimentary, and previously metamorphosed rocks change texture and composition when subjected to differing temperatures and pressures.
A rock's metamorphic grade (low, medium, or high grade) is related to the temperature and pressure at the time of contact or regional metamorphism. For instance, a low-grade metamorphic rock is a result of metamorphism at a low temperature and pressure.
All rocks tell a story. A rock's size tells something of its origin and how fast or slow the water moved that deposited the rock in its present location. A rock's roundness tells how long it traveled to get to its current location. The sorting (whether one size or various sizes) of the its constituent sediments tells whether the rock was transported by landslide or by glacier.
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