rock+cycle

** Rock Cycle ** TRANSITION TO IGNEOUS when rocks are pushed deep under the Earth's surface, they may melt into magma. If the conditions no longer exist for the magma to stay in its liquid state, it will cool and solidify into an igneous rock. A rock that cools within the earth is called intrusive and will cool very slowly, producing a coars-grained texture. As a result of volcanic activity, magma which is called lava may cool very rapidly that no crystals can form and result in a natural glass, such as obsidian. Any of the three main types of rocks (igneous, sedimentary & metamorphic rocks) can melt into magma and cool into igneous rock. TRANSITION TO SEDIMENTARY Rocks exposed to the atomosphere are variably unstable and subject to the processes of weathering and erosion. Weathering and erosion breaks the original rock down into smaller fragments and carries away dissolved material. This fragmented material accumulates and is buried by additional material. While an individual grain of sand is still a member of the class of rock it was formed from, a rock made up of such grains fused together is sedimentary. Sedimentary rocks can be formed from the lithification of these buried smaller fragments, the accumulation and lithification of material generated by living organisms or lithification of chemically precipitated material from a mineral bearing solution due to evaporation. Clastic rocks can be formed from fragments broken apart from larger rocks of any type, due to processes such as erosion or from organic material, like plant remains. Biogenic and precipitate rocks form from the deposition of minerals from chemicals dissolved from all other rock types. TRANSITION TO METAMORPHIC Rocks exposed to high temperatures and/or pressures can be changed physically or chemically to form a different rock, called metamorphic. Regional metamorphism refers to the effects on large masses of rocks over a wide area, typically associated with mountain building events within orogenic belt. These rocks commonly exhibit distinct bands of differing mineralogy and colors, called foliation. Another main type of metamorphism is caused when a body of rock comes into contact with an igneous intrusion that heats up this surrounding country rock. This //contact metamorphism// results in a rock that is altered and re-crystallized by the extreme heat of the magma and/or by the addition of fluids from the magma that add chemicals to the surrounding rock. Any pre-existing type of rock can be modified by the processes of metamorphism.