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Rock_Identification_13 - crystals perpendicular to...

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Figure 2,24 Generalized illustration of sedimentary environments. Although many environments exist on both the land and in the sea, only some of the most important are represented in this idealized diagram. (Photos by E. J. Tarbuck) Metamorphic Rock Identification Metamorphic rocks were previously igneous, sedimen- tary, or other metamorphic rocks that were changed by any combination of heat, pressure, and/or chemical fluids during the process of metamorphism. They are most often located beneath sedimentary rocks on the continents and in the cores of mountains. During metamorphism new minerals may form, and/or existing minerals can grow larger as metamor-
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phism becomes more intense. Frequently, mineral crystals that are elongated (like hornblende) or have a sheet structure (like the micas—biotite and muscovite) become oriented perpendicular to compressional forces. The resulting parallel, linear alignment of mineral
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Unformatted text preview: crystals perpendicular to compressional forces (stress) is called foliation (Figure 2.25). Foliation is unique to many metamorphic rocks and gives them a layered or banded appearance. Metamorphic rocks are divided into two groups based on texture—foliated and nonfoliated. These tex-tural divisions provide the basis for the identification of metamorphic rocks. Foliated Metamorphic Rocks The mineral crystals in foliated metamorphic rocks are either elongated or have a sheet structure and are arranged in a parallel or "layered" manner. During metamorphism, increased heat and pressure can cause the mineral crystals to become larger and the foliation more ob-vious. The metamorphic rocks in Figures 2.16-2.20 ex-hibit foliated textures. 21. From the rocks illustrated in Figures 2.16 and 2.18, was it the (slate, schist) resulted from more intensive heat and pressure?...
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