What are the kinds of rocks?
(1) Igneous rocksform from when hot, molten rock (magma) directly crystallizes and solidifies. The melt originates deep within the Earth near active plate boundaries or hot spots, then rises toward the surface. Igneous rocks are divided into two groups, intrusive or extrusive, depending upon where the molten rock solidifies — below ground, or above ground. (2) Sedimentary rocks are formed from pre-existing rocks (clastic or chemical) or pieces of once-living organisms (biogenic). They form from deposits that accumulate on the Earth’s surface. Sedimentary rocks often have distinctive layering or bedding. They need to be compressed so that they are cemented into individual rock units rather than just random layers of sediment. This comes from tectonic stress that does not involve large amounts of heat. (3) Metamorphic rocks started out as some other type of rock, but have been substantially changed from their original igneous, sedimentary, or earlier metamorphic form. Metamorphic rocks
