why do rocks look different from one another

The rock cycle is the natural process in which rocks transform from one rock type into another rock type over time, a type of natural recycling. Igneous rocks, which are formed from magma cooling underground, or lava above ground are formed from previous igneous, metamorphic, or sedimentary rocks which have become melted, usually as a result of plate collision and subduction. ------- When these igneous rocks are exposed to weathering and erosion, they break down into smaller particles that are transported by wind and water to a place of deposition, where they can form into sedimentary rock strata, through a process of lithification, where excess water is squeezed out by overburden pressures and the particles are cemented together by various minerals precipitating out of solution.

Igneous and metamorphic rocks can both be turned into sedimentary rocks in this way. ------- Igneous and sedimentary rocks can also be changed by heat and/or pressure into metamorphic rocks, by transforming their existing mineral structures into new minerals or realigning the existing minerals. There are different degrees of metamorphism, so even an existing metamorphic rock can become a different metamorphic rock. -------- If these metamorphic rocks are melted, then solidify, they become igneous rocks, and the cycle starts all over again.
Rocks can differ in many ways -- too many to list. Two examples:. Composition- The mineral composition is one way that rocks can differ. Some rocks, described as felsic, contain more silica and less iron and magnesium than mafic rocks.

Rocks can further be divided by the proportions of these and other elements that they contain. Method of formation- Rocks can form in three main ways. Igneous rocks are solidified from melt. The speed of cooling and the composition of the magma from which they are formed determine the type of igneous rock. For example, basalt and gabbro have approximately the same composition, but different cooling speeds. Gabbro and granite have similar cooling speeds, but different compositions. Sedimentary rocks are formed by the lithification of sediments or precipitates. Again, they can be further divided by the composition of the rocks from which they are formed, as well as by grain size. Additionally, the method of sedimentary formation (biochemical, chemical, or clastic) determines the type of sedimentary rock.

For example, limestone can be formed as a biochemical sedimentary rock (fossiliferous limestone), a chemical sedimentary rock (travertine), or a clastic sedimetary rock (clastic limestone). Metamorphic rock is formed when a rock undergoes pressure and/or heat without melting. The amount of heat or pressure as well as the direction of any applied pressure influences the type of metamorphic rock produced. The amount of time over which the rock is exposed to pressure or heat also affects the rock produced. For example, rocks such as gneiss experience differential pressure, which causes foliation to occur. In contrast, quartzite does not experience such differential pressure, and is not foliated.

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