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5100 West Henrietta Road • PO Box 92912 • Rochester, New York 14692-9012 • p: 800 962-2660 • wardsci.com The Rock Cycle ©2022 Ward's Science. All Rights Reserved. POSTER 470015-154 Lithification In the ideal cycle, sediments are transported to lower and lower elevations until they ultimately reach river flood plains and the ocean. Here they settle and accumulate in layers over thousands and millions of years. During this time, the thickness of the deposits can reach hundreds and even thousands of meters. With the buildup of overlying pressure, the layers compact and some grains may even recrystallize. This process of compaction, cementation, and recrystallization of sediments is known collectively as lithification. Weathering & Erosion Rocks and minerals at or near the earth's surface are affected by their interaction with air, water, changing temperatures, and living organisms. Called weathering, these processes gradually alter the rocks, causing them to change character, decay, and finally crumble into soil or loose rock debris (sediment). The work of gravity, moving water, ice, or air then transports these sediments from one place to another on the earth's surface. This weathering and transport of rock materials is called erosion. Melting If metamorphic rocks undergo still greater increases in temperature and pressure, they may eventually expe- rience melting and the formation of new magma. When this magma cools, igneous rock is formed, and the cycle has come full circle. Metamorphism As the cycle continues, the new sedimentary rocks may in turn be deeply buried by overlying sediments and rocks and sub- jected to increasing pressures, temperatures, and forces gener- ated by earth movements. These conditions may create changes in rock composition, texture, or internal structure through a pro- cess known as metamorphism. Cooling & Crystallization Magma solidifies through the process of crystallization. As cooling begins, mineral grains slowly begin to grow and may remain in solution for a time or settle out of the magma mixture. Lava cools rapidly, allowing little time for minerals to settle or react with the remaining liquid. Magma bodies at depth, on the other hand, cool and crystallize much more slowly. This allows a higher degree of chemical reaction to take place, and generally larger crystals to form. In all cases, the crystallization of magma forms igneous rock. Magma Magma is naturally occurring molten rock material generated beneath the earth's crust. When magma works its way to the surface through cracks and fissures in the earth's crust, it may explode violently to form layers of ash and cinders, or it may flow out as streams of molten material we call lava. L ith if i c a t ion M e l ti ng Cooli n g & C rystalli z a ti on W e at her i n g & Er o s i o n Igneous Rocks Metamorphic Rocks Sediments Sedimentary Rocks M et a m or p hism Igneous Rocks It's most probable that when the cycle began, all rocks on earth were igneous, having cooled from molten rock material. Igneous rocks are commonly classified according to their mineral composition and texture. Texture refers to the size, shape, and general arrangement of an igneous rock's interlocking mineral grains. These characteristics are often determined by the rate of magma cooling and the magma's overall viscosity. Pumice Rhyolite Granite What are rocks? Generally rocks are composed of inorganic, naturally formed crystalline solids called minerals. Minerals, in turn, are made up of an orderly arrangement of atoms which display a definite internal structure and a composition that is generally constant. The manner in which minerals form and the conditions leading to their association determine the types and classification of the resulting rocks. All rocks can be placed into one of three groups based on their mode of origin: igneous, sedimentary, and metamorphic. With time and changing conditions, any one of the rock types may be changed into some other form. The processes and events which affect the formation and development of igneous, sedimentary, and metamorphic rocks are known collectively as the Rock Cycle. As graphically displayed below, the outer circle of the Rock Cycle represents the complete cycle. If uninterrupted, the cycle continues around the outer margin of the circle from the formation of magma to igneous rocks to sediments to sedimentary rocks to metamorphic rocks and finally back to magma. The Rock Cycle, however, may be interrupted at various stages through the action of particular processes. This may lead, for example, to the direct metamorphism of igneous rock or to the melting of sedimentary rock to form new magma. The key to understanding the Rock Cycle is recognition of the ongoing processes which influence the development and transformation of the various rock types. Sediments The loose rock debris that originates from the weathering of rocks is transported and generally sorted over time and distance by particle size. These sediments have specific size classifications ranging from larger pebbles and gravel to smaller sand, silt, and clay-size particles. Clay Sand Gravel Sedimentary Rocks Through lithification, sediments are slowly hardened into sedimentary rock. Sedimentary rocks are generally classified based on the mode of origin of the constituent particles — specifically, whether they are chemical (precipitated), clastic (pre-existing rock and mineral particles), or organic (formed by organisms). A blanket of sedimentary rocks covers much of the earth's surface. However, in most areas it is a veneer only a few meters to a few hundred meters thick. Shale Sandstone Limestone Schist Marble Gneiss Metamorphic Rocks When preexisting rocks of any type are altered in the solid state due to pronounced changes of temperature, pressure, and chemical conditions below the earth's crust, the rocks are said to be metamorphosed. We refer to these "changed" rocks as metamorphic rocks. During this process, some rocks develop a definite parallel structure of flat or elongated mineral grains called foliation, while others simply show the effects of increased grain size due to recrystallization. What are rocks? Generally rocks are composed of inorganic, naturally formed crystalline solids called minerals. Minerals, in turn, are made up of an orderly arrangement of atoms which display a definite internal structure and a composition that is generally constant. The manner in which minerals form and the conditions leading to their association determine the types and classification of the resulting rocks. All rocks can be placed into one of three groups based on their mode of origin: igneous, sedimentary, and metamorphic. With time and changing conditions, any one of the rock types may be changed into some other form. The processes and events which affect the formation and development of igneous, sedimentary, and metamorphic rocks are known collectively as the Rock Cycle. As graphically displayed below, the outer circle of the Rock Cycle represents the complete cycle. If uninterrupted, the cycle continues around the outer margin of the circle from the formation of magma to igneous rocks to sediments to sedimentary rocks to metamorphic rocks and finally back to magma. The Rock Cycle, however, may be interrupted at various stages through the action of particular processes. This may lead, for example, to the direct metamorphism of igneous rock or to the melting of sedimentary rock to form new magma. The key to understanding the Rock Cycle is recognition of the ongoing processes which influence the development and transformation of the various rock types.

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