Phy-113-601-Lab4.pdf - naturally cemented together They...

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112 L A B O R AT O R Y 4 naturally cemented together. They also form when mineral crystals precipitate from water to form a rocky mass such as rock salt or cave stalactites. Metamorphic rocks are rocks deformed or changed from one form to another (transformed) by intense heat, intense pressure, and/or the action of hot fluids. This causes the rock to recrystallize, fracture, change color, and/or flow. As the rock flows, the flat layers are folded and the mineral crystals are aligned like parallel needles or scales. The Rock Cycle All rocks are part of a system of rock-forming processes, materials, and products that is often portrayed in a conceptual model called the rock cycle ( FIGURE 4.2 ). The rock cycle model explains how all rocks can be formed, deformed, transformed, melted, and reformed as a result of environmental factors and natural processes that affect them. Igneous Processes. An idealized path (broad purple arrows) of rock cycling and redistribution of matter is illustrated in FIGURE 4.2 , starting with igneous processes. If magma (from the mantle or lower crust) cools, then it solidifies into igneous rocks that are masses of glass or aggregates of intergrown mineral crystals. Sedimentary Processes. If these igneous rocks are uplifted, then sedimentary processes force other changes to occur. The igneous rocks are weathered (fragmented into grains, chemically decayed to residues, or even dissolved), eroded (worn away) and transported (moved to a new place), and later deposited to form sediment (an accumulation of chemical residues and fragmented rocks, mineral crystals, plants, or animals). Meteorites (dust and rocks from space) may be incorporated into the sediment. Sediment is lithified (hardened) into sedimentary rock as it compacts under its own weight or gets naturally cemented with crystals precipitated from water. Metamorphic Processes. If the sedimentary rock is subjected to metamorphic processes (intense heat, intense pressure, or the chemical action of hot fluids), then it will deform (fold, fracture, or otherwise change its shape) and transform (change color, density, composition, and/or general form) to metamorphic rock. And if the heat is great enough, then the metamorphic rock will melt (an igneous process) to form another body of magma that will begin the cycle again. Multiple Pathways Through the Rock Cycle. Of course, not all rocks undergo change along such an idealistic path. There are at least three changes that each rock could undergo. The arrows in FIGURE 4.2 Rocks and the Rock Cycle Most rocks are solid aggregates of mineral grains (par- ticles), either mineral crystals or clasts (broken pieces) of mineral crystals and rocks (e.g., pebbles, gravel, sand, and silt). There are, however, a few notable rocks that are not made of mineral grains. For example, obsidian is a rock made of volcanic glass, and coal is a rock made of plant fragments.
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