RocksGroup6

=​ What is a rock? A rock is solid that occurs naturally by minerals being bound together in some way. = = = =What are the three different types of rocks? The three types of rocks are igneous, sedimentary and metamorphic. They are named on the way that they are formed. = = = =What is an Sedimentary rock? When a sedimentary rock is formed sediments build up and are cemented together and create an organic material. There are three different kinds of sedimentary rocks. These are clastic, chemical (crystalline) and organic (bioclastic). The first kind of sedimentary rock which is a clastic sedimentary rock is formed from solid fragments of other rocks. The sediments that are found in these rocks are there from weathering of preexisting rocks. The different sizes of sediments going from largest to smallest are boulders, pebbles, sand, silt and clay. These fragmetns are moved by running water, waves, wind and glaciers. As a particle travels farther the more round the particle becomes. Lifhification forms sedimentary rocks and it is the compaction and cementation of rock fragments. When a mixture of larger rounded pebbles are cemented together it is called conglomerate. The next type of sedimentary rock is a chemical (crystalline) rock. Thsi is when dissolved minerals percipitate, or drop out of the water and is evvaporated. This usually is seen in a shallow sea enviroment.The results of this is a crystalline mass of intergrown mineral crystals. The last type of sedimentary rocks is a organic (bioclastic) sedimentary rock. This is the only type of sedimentary rock that fossils of once living plants or animals can be fouund. There are mand different features to sedimentary rocks. The first is fossils which are the evidence of plants and animals preserved in a rock. If it is a fossil then there will be remains or imprints of the once living animal or plant found in the rock. Another feature that can show it is a sedimentary rock is stratification. This is the arangement of visible layers, when type of sediments that are found in an area change then this causes a new type of sedimentary rock to form. Mud cracks also tell you that is is a sedimentary rock. Mud cracks develop when deposits of wet clay dry up and contract. Ripple marks are also a feature of sedimentary rocks. Ripple marks are formed by the action of winds, streams, waves, and currents on sand. The last three features of sedimentary rocks are nodules, concretions and geodes. Nodules are lumps of fine-grained silica. Concretions are round masses of calcuim carbonate that occur in the layers of shale. The last geodes, are the hollow spheres in which groundwater has deposited quartz or calcite crystals. Some ways to identify sedimetnary rocks are the grain size. You find this by looking at the crystal size and you can also look at the composition of the rock to help identify the rock. Examples of igneous rock: second rock picture - conglomerate which shows rounded fragments and contains pebbles and cobbles. first rock picture - bituminous coal which shows compacted plant remainos and has a grain size that can be microsopic or very coarse. = = = == == = = = = =[]= = = =What is an igneous rock? An igneous rock is formed by the cooling and hardening of moletn rocks. There are intrusive and extrusive igneous rocks. If an igneous rock is intrusive then it means that the rock formed below the Earths surface. Magma isthe molten rock beneath Earths surface. Intrusive igneous rocks cool slowly deep in the Earth. Because of this large crystals are formed. An intrusive igneous rock will be very course or coarse. If an igneous rock is extrusive then it means that the rock formed above Earhts surface. Lava is molten rock that pours out onto the Earths surface. When an igneous rock is extrusive then it cools very quickly and this causes the rock to have smaller crystals and not distinct mineral grains. An exturive igneous rock will have a fine texture. Some of these rocks will have a glassy texture. This occurs when the cooling is instantaneous. example: Obsidian. Sometimes gas bubbles are trapped because of the lava cooling quickly which causes the rock to have a vesicular texture. Another form of igneous rocks a porpyritic rocks. These rocks contain two stages of cooling. The first stage cools at a great depth beneath the earths surface which create large crystals and then the rock is still surrounded by magma. Then it is rushed to the surface and the remaining molten material around the rock cool quickly and form smaller, fine grained crystals. Some ways to identify igneous rocks are the texture of the rock. A rock can have a glassy texture, fine texture, coarse texture or very coarse texture. You can find this by looking at the size of the crystals on an igneous rock. You can also look to see the color of the rock to see wether it is mafic of felsic. Looking at the crystal size of the rock tells you wether the rock is intrusive or extrusive. If the rock has large crystals it is intrusive while if the rock has smaller crystals then the rock is extrusive. Another helpful thing to look at when trying to identify igneous rocks. Examples: first picture: obsidian which shows a glassy texture and is non vesicular. second picture: scoria which is fine and shows a vesicular texture. = = = == = = == = = = = = = = = = = = = = = = = = = =[][|ogy.about.com/cs/basics_roxmin/a/aa011804a.htm]l = =What is a metamorphic rock? A metamorphic rock is formed when a preexisting rock like a sedimentary or igneous rock are changed by heat and pressure. The rock has been changed by high temperatures and pressure combine to change the texture, mineral composition and chemcial composition. Metamorphism is when metamorphic rocks are formed in the lithoshpere which make the rocks more dense and less porous. Recrystallization takes place when the size of a minerals crystals are incresed either with or without changing the mineral composition. There are two different textural groups that metamorphic rocks are placed into. The first is foliation. When foliation occurs layers and bands are created on the rock. The foliation develops when pressure is applied from opposite directions. The foliation develops perpindicular to the pressure direction. The next texture that a metamorphic is being nonfoliated. If a rock is nonfoliated the the rock is most likely composed of a mineral that has blocky crystal shapes. Some examples of minerals that have blocky crystal shapes are marble and quarzite. There are three different types of metamorphism that can occur. The first is regional metamorphism. This occurs when high temperatures and pressure affect a large region of Earths crust. It is when large areas of rock are under intense heeat and pressure which cause them to change form. Foliation occurs here. Some effects that regional metamorphism can have are changes in mineral and rock types. Also, folding and deforming of rock layers that make up the area. Regional metamorphism tends to occur in mountanious areas. The second type of metamorphism that can take place is contact metamorphism. The is when hot magma forces its way into overlying rock and bakes the rocks in contact with it. This is when molten material comes in contact with solid rock. The final type of metamorphism that can occur is hydrothermal metamorphism and this is when very hot water reacts with rocks. Examples: first picture- gniess which shows a foliated texture. second picture quartzite which shows the metamorphism of quartz or sandstone. = = = =__[] <span style="font-family: 'Comic Sans MS',cursive; font-size: 90%;">​ __= = = <span style="font-family: 'Comic Sans MS',cursive; font-size: 90%;">What is the rock cycle? The rock cycle shows the formation, breakdown and reformation of a rock as a result of sedimentary, igneous and metamorphic processes.



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