ch11_2302 - Earth Materials • The Crust and its...

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Unformatted text preview: Earth Materials • The Crust and its Composition • Igneous Rocks • Sediments and Sedimentary Rocks • Metamorphic Rocks • The Cycle of Rock Change The Crust and its Composition oxygen and silicon account for about 75% of the earth's crust metallic elements iron, aluminum and the base elements account for most of the rest Figure11.1, p. 399 The Crust and its Composition the elements of the crust are combined in inorganic chemical compounds called minerals these minerals are mixed together in various proportions to form different rock classes rocks of the Earth's crust are grouped into three major classes: igneous, sedimentary and metamorphic rocks Igneous Rocks igneous rocks consist mainly of silicate minerals containing silicon, oxygen and metallic elements less dense felsic minerals dominate the igneous rocks of the upper crust while more dense mafic and ultramafic minerals dominate those of the lower crust magma that solidifies below the Earth’s surface and remains surrounded by older, preexisting rock is called intrusive igneous rock where magma reaches the surface, it emerges as lava, which solidifies to form extrusive igneous rock Felsic is a term used in geology to refer to silicate minerals , magmas , and rocks which are enriched in the lighter elements such as silicon , oxygen , aluminium , sodium , and potassium . The term combines the words " feldspar " and " silica ." Felsic minerals are usually light in color and have specific gravities less than 3. Common felsic minerals include quartz , muscovite , orthoclase , and the sodium-rich plagioclase feldspars . The most common felsic rock is granite . Mafic minerals are usually dark in color and have a specific gravity greater than 3. Common rock-forming mafic minerals include olivine , pyroxene , amphibole , biotite and other micas , augite and the calcium-rich plagioclase feldspars . Common mafic rocks include basalt and gabbro . Ultramafic (or ultrabasic) rocks are igneous and meta-igneous rocks with very low silica content (less than 45%), generally >18% Mg O, high Fe O, low potassium , and are composed of usually greater than 90% mafic minerals (dark colored, high magnesium and iron content). The Earth's mantle is considered to be composed of ultramafic rocks. Specific gravity is defined as the ratio of the density of a given substance to the density of water , when both are at the same temperature. Substances with a specific gravity greater than one are denser than water (and so will sink in it), and those with a specific gravity of less than one are less dense than water (and so will float in it). intrusive igneous rocks solidify below the Earth’s surface, they cool slowly and therefore develop larger mineral crystals visible to the eye extrusive igneous rocks cool very rapidly on the land surface or ocean bottom and thus develop...
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This note was uploaded on 06/01/2010 for the course GEOG 1F91 taught by Professor Nealpilger during the Fall '10 term at Brock University.

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ch11_2302 - Earth Materials • The Crust and its...

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