name three types of rocks and how are they formed?
Rocks are categorized into three distinct types based on their method of formation. The three types are igneous, sedimentary, and metamorphic. Early in Earth's history, all rock was igneous, having formed from the cooling of melt on the surface.
An igneous rock is simply a rock that has solidified from magma or lava upon cooling. Igneous rocks can be intrusive (solidified from magma underground) or extrusive (solidified from lava at or near the surface). The bulk of Earth's crust is formed from igneous rock. Examples of igneous rock include basalt, obsidian, rhyolite, granite, diorite, gabbro, and pumice.
A sedimentary rock is one that is formed by the accumulation of small to large sediment particles derived from all three types of rock and in some cases organic material, and undergoes compaction, cementation, or evaporation from/precipitation from a saturated mineral solution. Sedimentary rock is classified as organic, (derived from organisms), clastic (formed from any size particle of preexisting rock), or non-clastic (also referred to as chemical), where the sedimentary rock is formed from the evaporation of a solution that is saturated with mineral compounds. Examples of organic sedimentary rocks are coal and limestone. Examples of clastic sedimentary rocks are conglomerate and shale. Examples of non-clastic or chemical sedimentary rocks are rock gypsum and rock salt.
A metamorphic rock is an igneous, sedimentary, or another metamorphic rock that has either been squeezed by incredible pressures deep underground and/or has been exposed to very high temperatures, altering its structure, mineral alignment, or chemical composition. Metamorphic rocks are classified as contact (from proximity to a magmatic intrusion) or regional (resulting from deep burial and pressures from plate collisions. Metamorphic rock is also classified as foliated or non-foliated; foliation being the parallel alignment of the constituent minerals in bands that are perpendicular to the applied pressure. Metamorphic rocks can also be described by the grade of metamorphism which has taken place from low to high, high being the closest to the next stage in the rock cycle, melting. Examples of metamorphic rock are slate, quartzite, marble, phyllite, schist, and gneiss.
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