Minerals in geology (2)

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ROCK AND MINERAL TYPES • Minerals are chemical compounds, sometimes specified by crystalline structure as well as by composition, which are found in rocks (or pulverized rocks, known as sand) • Rocks consist of one or more Minerals, and fall into three main types depending on their origin and previous processing history: o Igneous rocks are ones which have solidified directly from a molten state, such as volcanic lava o Sedimentary rocks are ones which have been remanufactured from previously existing rocks, usually from the products of chemical weathering or mechanical erosion, without melting o Metamorphic rocks are ones which result from processing, by heat and pressure (but not melting), of previously existing sedimentary or igneous rocks COMMON MINERALS IN THE EARTH • QUARTZ (Silica) SiO2 • CORUNDUM (Alumina) Al2O3 • HEMATITE • CALCITE • DOLOMITE • GYPSUM OLIVINE (Mg,Fe)2SiO4 • PYROXENE (Mg,Fe)SiO3 • AMPHIBOLE (Ca2Mg5)Si8O22(OH)2 • FELDSPARS Albite Fe2O3 CaCO3 CaMg(CO3)2 CaSO4 • FLUORITE CaF2 PYRITE FeS2 • • Orthoclase Anorthite • KAOLINITE NaAlSi3O8 KAlSi3O8 CaAl2Si2O8 Al2Si2O5(OH)4 ROCK AND MINERAL TYPES • Examples of Igneous Rocks and their constituent minerals include: • Basalt, Gabbro, Rhyolite, Granite o Feldspar, Quartz, Amphibole, Pyroxine, Olivine • Basalt and Gabbro differ not in composition, but in crystallinity; likewise Rhyolite and Granite • Basalt and Gabbro differ in relative composition, of the five major constituents above, from Rhyolite and Granite • Basalt and Rhyolite have small crystals because they are erupted by volcanoes and cool rapidly from the molten state • Gabbro and Granite have large crystals because they cool slowly from the molten state, underground ROCK AND MINERAL TYPES • Basalt/Gabbro and Rhyolite/Granite differ in their proportions of the minerals listed above: o Basalt and Gabbro consist mostly of Pyroxine and Olivine Since these minerals consist largely of magnesium and iron silicates, these rocks are sometimes called mafic o Rhyolite and Granite consist mostly of Feldspar, Quartz, and Amphibole They are, hence, sometimes called felsic rocks o There is a continuous range in composition between the two extremes, of both composition and crystallinity ROCK AND MINERAL TYPES • Examples of Sedimentary Rocks include Limestone, Sandstone, and Shale o Limestone is mostly Calcite (CaCO3) produced by chemical weathering of Feldspar and other silicate minerals Limestone also is produced from the shells and skeletons of sea life (e.g plankton and coral) o Sandstone and Shale are produced from sand (mostly quartz) and clay minerals (such as kaolinite), which result from mechanical and chemical weathering of igneous rocks • Examples of Metamorphic Rocks include Marble (from Limestone) and Slate (from Shale) The Rock Cycle
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