Rocks are solid aggregate of minerals andor mineraloids that forms the Earths crust through natural processes (Park, et. al., 2004). Rocks are classified according to the process of their formation, mineral and chemical composition and texture and size of the constituent particles. In general rocks are of three different types, namely, igneous, sedimentary and metamorphic.
Igneous rocks are those which solidified from molten or partly molten material through exothermic process. All rocks originated from igneous rocks which in turn originated from the Earths mantle molten magma. As magma cools, ions arrange themselves into orderly patterns during crystallization. When magma crystallizes slowly deep below the Earths surface, plutonic (intrusive) igneous rocks are formed while volcanic (extrusive) igneous rocks are formed when magma crystallizes quickly at spreading centers and volcanic eruptions.
Igneous rocks are associated with plate tectonics (Faure, 2001). They are found across specific places of the earth according to plate tectonics processes and conditions. Fractionation occurs at divergent and convergent plate boundaries. The former type of boundaries are mostly underwater and from here magma surfaces out onto the ocean floor to form new oceanic lithosphere.
Source httpcsmres.jmu.edugeollabFichterIgnRxdisthtml.html
In the process the parent rock of the earths interior fractionates to form mafic igneous rocks, such as basalt and gabbro. On the other hand, at convergent boundaries, diorite and granite are formed as part of the ocean lithosphere descends into the earth again, where it heats up and fractionally melts.
The second type of rocks are sedimentary rocks which are formed by the accumulation of sediment, mineral particles that have either settled from a state of suspension in air or water or have been precipitated from a state of solution (Park, et.al., 2004). They are called secondary because of the accumulation of small fragments broken off of pre-existing igneous, sedimentary and metamorphic rocks. These rocks are subject to weathering, which can either change their physical appearance (mechanical weathering) or their compound composition (chemical weathering) during the process. Forces of erosion play an important part here as they wear away rocks to form sediments. Materials are transported around Earths surface by a mobile agent like wind or water. As these forces lose energy, the sediments settle out of the air or water. The settling takes place, the larger heavier pieces having to settle out first.
The smallest fragments travel farther and settle out last. This process of settling out is called deposition. These sediments can be compacted and cemented through lithification. Compaction occurs after the sediments have been deposited. The weight of the sediments squeezes the particles together. As more and more sediments are deposited the weight on the sediments below increases. Waterborne sediments become so tightly squeezed together that most of the water is pushed out. Cementation happens as dissolved minerals become deposited in the spaces between the sediments. These minerals act as glue or cement to bind the sediments together.
Sedimentary rocks are classified in three main groups clastic, chemical and organic. Clastic sedimentary rocks are formed from broken bits and pieces of other existing rocks that settle out of water or air. Chemical sedimentary rocks are formed from chemicals or elements dissolved in water. Evaporites, carbonates and siliceous rocks are three types of sedimentary rocks. Organic sedimentary rocks are composed of organic matter in the form of plant fragments.
Last, metamorphic rocks are those which have undergone marked transformation, in response to heat, pressure or chemical alteration. These factors can change pre-existing rocks through the process called metamorphism. Rocks remain solid during the process despite the alteration in their mineral composition and texture. During the process, two minerals can react, and their ions can diffuse across grain boundaries, resulting in a new mineral. Alternatively, complex minerals may break down into simpler ones. Rocks gain foliation or alignment as minerals align into bands. As temperature and pressure increase, grain size increases and texture coarsens.
Metamorphic rocks are classified according to intensity of metamorphism. They may be foliated rocks which are all from sedimentary rock called shale. Shale is metamorphosed to different grades it can form slate, phyllite, schist or gneiss. On the other hand, examples of non-foliated rocks are marble, quartzite, hornfels. Non-foliated rocks are metamorphic rocks which do not have wavy layers.
Igneous, sedimentary and metamorphic rocks gradually and continuously change into one another (Annenberg Media Learner Organization). Cooling of molten magma forms intrusive igneous rocks below the Earths surface and extrusive igneous rocks above the surface. Surface rocks eventually erode into particles, which are washed into the seas and deposited as sediment. Compaction and cementation of accumulated sediment form sedimentary rocks. Accumulation of more sediment forces these rocks into the hot plastic mantle where they melt, mix with other materials, rise and solidify again. Combined heat and pressure ma change igneous and sedimentary rocks into metamorphic rocks. These continual conversion from one type of rock to another are collectively termed the rock cycle.
Igneous rocks are those which solidified from molten or partly molten material through exothermic process. All rocks originated from igneous rocks which in turn originated from the Earths mantle molten magma. As magma cools, ions arrange themselves into orderly patterns during crystallization. When magma crystallizes slowly deep below the Earths surface, plutonic (intrusive) igneous rocks are formed while volcanic (extrusive) igneous rocks are formed when magma crystallizes quickly at spreading centers and volcanic eruptions.
Igneous rocks are associated with plate tectonics (Faure, 2001). They are found across specific places of the earth according to plate tectonics processes and conditions. Fractionation occurs at divergent and convergent plate boundaries. The former type of boundaries are mostly underwater and from here magma surfaces out onto the ocean floor to form new oceanic lithosphere.
Source httpcsmres.jmu.edugeollabFichterIgnRxdisthtml.html
In the process the parent rock of the earths interior fractionates to form mafic igneous rocks, such as basalt and gabbro. On the other hand, at convergent boundaries, diorite and granite are formed as part of the ocean lithosphere descends into the earth again, where it heats up and fractionally melts.
The second type of rocks are sedimentary rocks which are formed by the accumulation of sediment, mineral particles that have either settled from a state of suspension in air or water or have been precipitated from a state of solution (Park, et.al., 2004). They are called secondary because of the accumulation of small fragments broken off of pre-existing igneous, sedimentary and metamorphic rocks. These rocks are subject to weathering, which can either change their physical appearance (mechanical weathering) or their compound composition (chemical weathering) during the process. Forces of erosion play an important part here as they wear away rocks to form sediments. Materials are transported around Earths surface by a mobile agent like wind or water. As these forces lose energy, the sediments settle out of the air or water. The settling takes place, the larger heavier pieces having to settle out first.
The smallest fragments travel farther and settle out last. This process of settling out is called deposition. These sediments can be compacted and cemented through lithification. Compaction occurs after the sediments have been deposited. The weight of the sediments squeezes the particles together. As more and more sediments are deposited the weight on the sediments below increases. Waterborne sediments become so tightly squeezed together that most of the water is pushed out. Cementation happens as dissolved minerals become deposited in the spaces between the sediments. These minerals act as glue or cement to bind the sediments together.
Sedimentary rocks are classified in three main groups clastic, chemical and organic. Clastic sedimentary rocks are formed from broken bits and pieces of other existing rocks that settle out of water or air. Chemical sedimentary rocks are formed from chemicals or elements dissolved in water. Evaporites, carbonates and siliceous rocks are three types of sedimentary rocks. Organic sedimentary rocks are composed of organic matter in the form of plant fragments.
Last, metamorphic rocks are those which have undergone marked transformation, in response to heat, pressure or chemical alteration. These factors can change pre-existing rocks through the process called metamorphism. Rocks remain solid during the process despite the alteration in their mineral composition and texture. During the process, two minerals can react, and their ions can diffuse across grain boundaries, resulting in a new mineral. Alternatively, complex minerals may break down into simpler ones. Rocks gain foliation or alignment as minerals align into bands. As temperature and pressure increase, grain size increases and texture coarsens.
Metamorphic rocks are classified according to intensity of metamorphism. They may be foliated rocks which are all from sedimentary rock called shale. Shale is metamorphosed to different grades it can form slate, phyllite, schist or gneiss. On the other hand, examples of non-foliated rocks are marble, quartzite, hornfels. Non-foliated rocks are metamorphic rocks which do not have wavy layers.
Igneous, sedimentary and metamorphic rocks gradually and continuously change into one another (Annenberg Media Learner Organization). Cooling of molten magma forms intrusive igneous rocks below the Earths surface and extrusive igneous rocks above the surface. Surface rocks eventually erode into particles, which are washed into the seas and deposited as sediment. Compaction and cementation of accumulated sediment form sedimentary rocks. Accumulation of more sediment forces these rocks into the hot plastic mantle where they melt, mix with other materials, rise and solidify again. Combined heat and pressure ma change igneous and sedimentary rocks into metamorphic rocks. These continual conversion from one type of rock to another are collectively termed the rock cycle.
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