F13 quiz 1 condensed notes

Igneous rocks from the latin fireformed originated

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Unformatted text preview: we have (1 x +4) [for silicon] + (2 x –2) [for oxygen] = 0; quartz is electrically neutral. In most silicate minerals, both factors (i) and (ii) stated above contribute toward electrical neutrality. We may have isolated tetrahedrons (ex. olivine), single chains (ex. the pyroxene family), double chains (ex. the amphibole family), sheets of Si ­O tetrahedrons (ex. the mica family or clay mineral family), or complex framework structures (as in quartz or the feldspar family of minerals). The resemblance between atomic structure and physical properties of silicate minerals is especially striking in the sheets present in mica minerals. Olivine, pyroxene, amphibole, and biotite mica are further distinguished as having lots of iron (Fe) and magnesium (Mg); they are called ferromagnesian minerals and are characteristically dark ­colored, dense minerals. In contrast, muscovite mica, varieties of feldspar, and quartz are not ferromagnesian minerals; instead of iron and magnesium, the associated cations may be aluminum, potassium, sodium, or calcium. There is more feldspar in the earth’s crust than all other minerals put together. Some other classes of minerals include native elements such as gold and sulfur that are composed of atoms of a single element. Carbonates are based on the carbonate anion (CO32 ­) and include the important mineral calcite. Oxides (ex. hematite Fe2O3) and sulfides (ex. pyrite FeS2, PbS) consist of metallic cations bonded to oxygen and sulfide (S2 ­), respectively, and include important weathering products and ore minerals. Sulfates, like gypsum, are based on the tetrahedral sulfate anion (SO4)2 ­. LECTURE 4: IGNEOUS ROCKS Atoms comprise crystals of minerals, and one or more minerals comprise most igneous, sedimentary, and metamorphic rocks. Igneous rocks (from the Latin: “fire ­formed”) originated from cooling and crystallization of silicate minerals from a molten mass called magma. Magma may be quite complex, consisting of liquid silicate material, plus already solidified crystals, plus dissolved volatiles, chiefly H2O. Magma is typically created in isolated chambers deep within the crust and upper mantle. Magma may have reached the surface to become lava and form extrusive (volcanic) rock, or it may have ascended toward the surface but became lodged at depth to crystallize as intrusive (plutonic) igneous rock. How is magma created? One obvious way is to raise the temperature of a rock beyond its melting point. Second, if a hot but solid rock is moved from great depth in the earth (higher pressure) up towards the earth’s surface (lower pressure), its volume expands, causing decompression melting, which can occur even if the tempera...
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This document was uploaded on 03/03/2014 for the course GEO 303K at University of Texas at Austin.

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