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Unit 1 Lesson 2 The Rock Cycle. Unit 1 Lesson 2 The Rock Cycle. How are rocks classified?. Rock is a naturally occurring solid mixture of one or more minerals and may also include organic matter.
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Unit 1 Lesson 2 The Rock Cycle How are rocks classified? • Rock is a naturally occurring solid mixture of one or more minerals and may also include organic matter. • Most rock is made of minerals, but some rock is made of non-mineral material that is not organic, such as glass. • Scientists divide rock into three classes: igneous, sedimentary, and metamorphic, and each class can be further divided into more specific types of rock. • Rocks are always changing through time and anytype of rock can change into another type.
Unit 1 Lesson 2 The Rock Cycle How are rocks classified? • To determine how to classify rocks, scientists observe their composition and texture. • The minerals a rock contains determine the composition, or makeup, of that rock. • The size, shape, and positions of the grains that make up a rock determine a rock’s texture. • The rock may be coarse-grained or fine-grained, depending on whether the grains are visible with one’s eyes or with a hand lens or microscope.
Unit 1 Lesson 2 The Rock Cycle Fine-Grained Coarse-Grained
Unit 1 Lesson 2 The Rock Cycle Igneous Rock • Magma is molten rock that forms in Earth’s crust under the surface. When magma cools and solidifies, it forms igneous rock in the crust. • Magma that reaches Earth’s surface is called lava. Igneous rock also forms when lava cools and solidifies on Earth’s surface. Lava Magma
Unit 1 Lesson 2 The Rock Cycle The two types of igneous rock • When magma intrudes, or pushes into surrounding rock below Earth’s surface, and cools, it forms intrusive igneous rock.
Unit 1 Lesson 2 The Rock Cycle • Magma usually cools very slowly, and the minerals form large, visible crystals. • Therefore, intrusive igneous rock generally has a coarse-grained texture. Intrusive Igneous Rocks Granite Gabbro
Unit 1 Lesson 2 The Rock Cycle • Igneous rock that forms when lava erupts, or extrudes, onto Earth’s surface is called extrusive igneous rock. • As lava cools quickly, there is little time for crystals to form, and extrusive igneous rocks have a fine-grained texture. • Obsidian, often called volcanic glass, is an extrusive rock that cools so rapidly that no crystals form.
Unit 1 Lesson 2 The Rock Cycle Extrusive Igneous Rocks Basalt Rhyolite Obsidian
Unit 1 Lesson 2 The Rock Cycle Sedimentary Rock • Sedimentary rock is formed by processes that occur mainly at or near Earth’s surface. • Based on the way that they form, scientists classify sedimentary rocks as clastic, chemical, and organic sedimentary rock. • Clastic sedimentary rock form from the burial, compaction, and cementation of sediment. • Organic sedimentary rock form the same way as clastic, but they form from the remains, or fossils, of once-living plants and animals. • Chemical sedimentary rocks form from evaporation.
Unit 1 Lesson 2 The Rock Cycle Clastic and Organic Sedimentary Rock • The processes that form clastic and organic sedimentary rock include weathering, erosion, deposition, burial, compaction, and cementation. • Weatheringis the process by which rock is broken down into sediment by water, wind, ice, and changes in temperature. • Erosionis the process by which sediment is moved from one place to another by water, wind, ice & gravity. • Sediment comes to rest by a process called deposition.
Unit 1 Lesson 2 The Rock Cycle • Rock and sediment that is buried is then squeezed, or compacted by the weight of rock or layers of sediment above it. • The layers are then “glued” or cemented together by other minerals, such as halite, calcite and/or quartz.
Unit 1 Lesson 2 The Rock Cycle Clastic Sedimentary Rock • The size of the sediment, or clasts, that makes up the rock is used to classify clastic sedimentary rocks as fine-, medium-, or coarse-grained. Shale Fine-Grained Sandstone Medium-Grained Breccia Coarse-Grained
Unit 1 Lesson 2 The Rock Cycle Organic Sedimentary Rock • One type of organic sedimentary rock forms from the remains of once-living aquatic animals. • Over time, the skeletons of marine organisms, made of calcium carbonate, collect on a lake or ocean floor. • These animal remains, together with sediment, are eventually buried, compacted, and cemented together to form limestone.
Unit 1 Lesson 2 The Rock Cycle • Another type of organic sedimentary rock forms from the remains of once-living plants that lived in swamps. • Over time, dead plant matter was covered up by sediment, stopping the aerobic decaying process. Anaerobic decay takes over turning the plant matter into peat. • As more sediment piled up, increasing pressure compressed the peat, squeezing out water and other compounds and coal begins to form. As heat and pressure increases the type and quality of coal changes.
Unit 1 Lesson 2 The Rock Cycle Organic Sedimentary Rocks Coal (C240H90O4NS) Fossiliferous Limestone (CaCO₃)
Unit 1 Lesson 2 The Rock Cycle Chemical Sedimentary Rock • Chemical sedimentary rock forms when water, which usually contains dissolved minerals like calcium chloride (CaCl₂), sodium chloride (NaCl), calcium sulfate (CaSO₄), evaporates. • As water evaporates, the minerals in it become concentrated, precipitate out of solution, and crystallize. Rock Salt Sodium Chloride (NaCl) Gypsum Calcium Sulfate (CaSO₄)
Unit 1 Lesson 2 The Rock Cycle Metamorphic Rock • As a rock is exposed to high temperature and/or pressure, the crystal structures of the minerals in the rock change to form new minerals. • This process results in the formation of metamorphic rock, with a foliated (layered or banded) or nonfoliated texture. • During metamorphism, mineral grains or crystals may change in size or the mineral may change in composition.
Unit 1 Lesson 2 The Rock Cycle Foliated Metamorphic Rock • Foliation occurs through regional metamorphism (when the pressure is greater in one direction). This causes the minerals in the original rock to realign themselves with the long and flat minerals aligning perpendicular to the greatest pressure direction. This gives the rock a striped and/or layered look. Realignment of the minerals Gneiss Slate
Unit 3Lesson 3 Three Classes of Rock Non-Foliated Metamorphic Rock • Metamorphic rocks that do not have mineral grains that are aligned in planes or bands are called nonfoliated. • Non-foliation occurs through contact metamorphism, where the rocks come into direct contact with magma and lava, subjecting them to very high temperatures, but not hot enough to melt them. • Nonfoliated metamorphic rocks are commonly made of one or only a few minerals. Marble Hornfels
Unit 1 Lesson 2 The Rock Cycle The Rock Cycle • Over millions of years, any of the three rock types can be changed into another of the three types. • The series of processes by which rock changes from one type to another is called the rock cycle. • A rock’s identity can be changed by factors such as temperature, pressure, weathering, and erosion.
Unit 1 Lesson 2 The Rock Cycle • Igneous rock that is exposed can break down into sediment. Beneath Earth’s surface, it can change into metamorphic rock. • With temperature and pressure changes, sedimentary rock can become metamorphic rock, or it may melt and become igneous rock. • Under certain temperature and pressure conditions, metamorphic rock can melt into magma and then form igneous rock or form a different metamorphic rock.
Unit 1 Lesson 2 The Rock Cycle What happens in each part of the rock cycle? 1. Weathering, Erosion, Deposition, Compaction & Cementation Igneous Rock Sedimentary Rock Cooling 4. 3. Melting 2. Temperature & Pressure Magma Metamorphic Rock
Unit 1 Lesson 2 The Rock Cycle Tectonic plate motions & the rock cycle • Tectonic plate motions can move rock around, leading to changes in the rock. These plate motions can move rock up or down. • Upliftis the rising of regions of the crust to higher elevations, increasing the rate of weathering and erosion. • Subsidenceis the sinking of regions of the crust to lower elevations, producing basins where sediment is deposited. • A rift zoneis a set of deep cracks that form between two tectonic plates that are pulling apart.
Unit 1 Lesson 2 The Rock Cycle Subsidence
Unit 3Lesson 2 The Rock Cycle Rift Zone • Blocks of crust in the center of the rift zone subside, and molten rock below Earth’s surface rises up. Rift Zone
