These intermediate rocks may form in geologic structures such as sills, dikes, and stocks. Magma that cools and solidifies at medium depths, porphyry textures or a mix of fine and coarse grains result in the hypabyssal rock such as andesite. If the magma cools and solidifies after moving up to the surface, aphanitic textures or fine crystal grains result in the extrusive rock such as basalt. If magma cools and solidifies at great depth, phaneritic textures or large crystal grains result in the intrusive rock such as granite. Igneous rock solidifies from molten material or emanating volatile constituents, hot aqueous or gaseous solutions and are broadly grouped as plutonic/intrusive, hypabyssal/intermediate, and volcanic/extrusive rocks. Sedimentary origins, Texture and the Wentworth Scale, Sedimentary Rock,.The chemical sedimentary rock types include opal, chert, iron-oxides, oolitic limestone, rock salt, bauxite, etc. Chemical rocks form from precipitation of low temperature/pressure minerals in saline or freshwater solutions onto a depositional surface or within sediment pores. This produces sediment with lithification accomplished by compaction and examples include coal and oil shales. The accumulation of carbon or hydrocarbon-rich sediments takes place in stagnant, oxygen-poor environments. Organic biogenic rocks are derived from decomposition of plant and animal tissues. These organisms are abundant in shallow, warm, clear seas, and are quickly cemented and may undergo mineralogical and textural diagenesis to create rocks such as limestone and chert. Bioclastic rocks are created from the hard skeletal parts of corals, mollusks, brachiopods, echinoderms, sponges, radiolaria, and other marine invertebrates. Biogenic rocks form directly or indirectly from organisms and are subdivided into bioclastic and biogenic. Clastic texture is described by size such as clay, silt, sand, gravel, etc., according to the Wentworth Scale, and includes rock types such as shale, sandstone, and conglomerate. Clastic or detrital rocks are composed of mineral grains produced by the weathering and erosion of preexisting igneous, metamorphic, or sedimentary rocks, all derived from land. Sedimentary groups are clastic (detrital), biogenic, and chemical. They are grouped according to depositional environments or source area of sediments. Sedimentary rocks are formed at or near the surface in layers of mineral grains that compact and cement into solid rock. Sedimentary Rock Igneous Rock Metamorphic Rock Identification Clues Rock Pictures Website Links Texture is the size, shape, and arrangement of mineral grains, while characteristic mineral components vary with environments and conditions of formation. Identifying texture and mineral components are key to naming rocks. Rocks are a natural aggregate of minerals and are classified into sedimentary, igneous, and metamorphic. Photo by S.W Aber Photo date June 5, 2009 Raton Basin and Southern Rocky Mountains of Colorado Identifying Rocks from the Flint Hills of Kansas, Rocks -GO 547 Field Geology - May/June 2009 Field Geology 2009:
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