The properties geologist use to classify rocks include color and crystal size. The color of the rock indicates the minerals it contains, but it is not always reliable. In the other hand, the size of the crystal or the particles it contain is. The particles inside rock makes its texture which reveals what it’s made out of and how or where it formed. Rocks are classified into three major groups- igneous, sedimentary, and metamorphic- based on how they form.
Igneous Rocks
Igneous Rocks
An igneous rock is formed from magma, a mixture of molten rock and gases which forms underground. Igneous rocks forms when molten material cools and solidifies either inside Earth or at the surface. When an igneous rock forms under ground is called intrusive rock and when it forms on the surface it is called an extrusive rock. Intrusive rocks slowly cool down allowing the crystals to grow large and it has a coarse-grained texture. Extrusive rocks cool down quickly so the crystal do not grow and it gives a fine-grained texture. The rocks composition depends on the magma’s composition. Magma is rich in iron and magnesium which produces dark dense rocks.
An igneous rock is formed from magma, a mixture of molten rock and gases which forms underground. Igneous rocks forms when molten material cools and solidifies either inside Earth or at the surface. When an igneous rock forms under ground is called intrusive rock and when it forms on the surface it is called an extrusive rock. Intrusive rocks slowly cool down allowing the crystals to grow large and it has a coarse-grained texture. Extrusive rocks cool down quickly so the crystal do not grow and it gives a fine-grained texture. The rocks composition depends on the magma’s composition. Magma is rich in iron and magnesium which produces dark dense rocks.
Clastic RockChemical Sedimentary RockOrganic Rock |
Sedimentary Rocks
Sediment comes from rocks or living organism and they are carried away by running water. Rivers carry sand, mud, and dissolved minerals into the ocean, which is deposited into the ocean floor. Sedimentary rock is a rock that forms overtime as sediment is squeezed and cemented together. Geologists classify sedimentary rocks into three main groups according to how they form: clastic rocks, chemical rocks, and organic rocks. Clastic rocks are sedimentary rocks that forms from the broken fragments of other rocks, which is usually held together by cement. Clastic rocks are classified on the average size of fragment it contains. If the rock contains gravel and pebble it is called conglomerate. Other clastic rocks a made from smaller particles, sandstone is formed from grains of sand. Sediment primary made of mud or silt is mudstone. Chemical sedimentary rocks form when minerals precipitate out of solution. minerals dissolved from rainwater gets carried down by river into the ocean. Then the ocean evaporates until the mineral sinks into the ocean floor. Chemical rocks can be found on land where lands are covered with thick layer of salt. Organic Rocks are from marine animals such as coral, clams, and mussels extract calcium carbonate from the ocean to form their skeleton and shell. Over time small fragments contract and cement to form limestones. |
Metamorphic Rocks
Metamorphic Rocks
Metamorphic rocks form when a rock is transformed by heat, pressure, or chemical reactions. Most metamorphic rocks form under high temperatures and pressures deep underground. Metamorphism can result in a rock with a mineral content different from the original. The heat deep inside Earth allows to recrystallize, and small crystals to enlarge. As chemical changes occur, new minerals replace the original. Metamorphism also changes the texture of the rock since sedimentary and igneous rocks are distributed randomly. Foliated rock are metamorphic rocks with crystal arranged in parallel layers.
Metamorphic rocks form when a rock is transformed by heat, pressure, or chemical reactions. Most metamorphic rocks form under high temperatures and pressures deep underground. Metamorphism can result in a rock with a mineral content different from the original. The heat deep inside Earth allows to recrystallize, and small crystals to enlarge. As chemical changes occur, new minerals replace the original. Metamorphism also changes the texture of the rock since sedimentary and igneous rocks are distributed randomly. Foliated rock are metamorphic rocks with crystal arranged in parallel layers.
The Rock Cycle
Rock cycle is a series of process in which rocks continuously change the type to one another. In the rock cycle forces within Earth and at the surface cause rocks to change form. Granite is broken into sand and the river carries it to the ocean floor, and becomes a sedimentary rock sandstone. Then the sandstone gets pushed deep underground and changes into a metamorphic rock quartzite. Then it could be heated and become an igneous rock.