Misc

Lashawone Powell

October 6, 2005

SCI 2144

The three major types of rocks, igneous, sedimentary, and metamorphic rocks are interrelated by a series of natural processes. Igneous rocks form from the cooling and crystallization of hot molten lava and magma. Igneous rocks undergo weathering and erosion to form sediments. Igneous rock can form from magma being brought to the surface by volcanic eruption or it can form beneath the surface. Sediments are deposited and lithified by compaction and cementation to form sedimentary rocks. Unconsolidated sediment is the precursor of sedimentary rock. Sedimentary rock becomes buried by additional sedimentary deposition, and when they are deep within the Earth, they are subjected to heat and pressure which causes them to become metamorphic rocks. With further burial and heating, the metamorphic rocks begin to melt. When heat and pressure below the Earth's surface become high enough, metamorphic rock is formed. Partially molten metamorphic rocks are known as migmatite. As melting proceeds with increasing temperatures and depths of burial, eventually the rock becomes molten and becomes magma, which cools and crystallizes to form plutonic igneous rock, or which is erupted onto the Earth's surface as lava, and cools and crystallizes to form volcanic igneous rock.

The rock cycle starts with molten rock (magma), which cools and forms igneous rocks. These rocks get uplifted as part of mountain-building and then begin to weather and erode. The eroded material is carried away by rivers, wind, glaciers, and other means and deposited elsewhere as sediments. These sediments then are buried and lithified into sedimentary rocks. Then these sedimentary rocks are buried, subjected to heat, pressure, and fluids, and become metamorphic rocks. Eventually, these metamorphic rocks may be heated to the point where they again melt into magma. This is a process that takes millions of years to take place. It is a process that can not be seen or produced as a tourist attraction; however some of the effects of this process left over thousands of years ago are evident in places like Yellowstone National park or the mountainous regions of Hawaii.