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Earth MaterialsImages from Strahler and Strahler, 2005
• 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 (from feldspar and silica) dominate the igneous rocks of the upper crust while more dense mafic and ultramafic (iron and magnesium) 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
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 smaller, microscopic size crystals
Igneous 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
Figure11.4, p. 401
Igneous RocksIntrusive (plutonic) igneous rocks
granite: felsic intrusive igneous rock (same minerals as rhyolite)
diorite: intermediate intrusive igneous rock
(same minerals as andesite)
gabbro: mafic extrusive igneous rock (same minerals as basalt)
peridotite: ultramafic (olivine rich)
Figure11.4, p. 401
Igneous RocksExtrusive (volcanic) igneous rocks
rhyolite: felsic extrusive igneous rock (same minerals as granite)
andesite: intermediate extrusive igneous rock
(same minerals as diorite)
basalt: mafic extrusive igneous rock (same minerals as gabbro)
Figure11.4, p. 401
Plutonic Rock in N. America
http://upload.wikimedia.org/wikipedia/commons/1/1a/North_america_rock_plutonic.jpg
Volcanic Rock in N. America
http://upload.wikimedia.org/wikipedia/commons/f/fa/North_america_rock_volcanic.jpg
Igneous Rocksa body of intrusive igneous rock is called a pluton (granite typically accumulates in enormous plutons, called batholiths extending down several kilometers and occupying an area of several thousand square kilometers)
a sill is a plate-like pluton formed when magma forces its way between two preexisting (usually sedimentary) rock layers
Figure 11.9, p. 404
Igneous Rocks
a dike is a wall-like pluton formed when a vertical rock fracture is forced open by magma
magma entering small, irregular, branching fractures in the surrounding rock solidifies in a branching network of thin veins
Figure 11.9, p. 404
mineral alteration occurs when the minerals in igneous rocks are transformed chemically into new minerals that are more stable at or near the Earth’s surface
processes of mineral alteration include oxidation, hydrolysis, and solution
in the process of mineral alteration, solid rock is weakened, softened, and fragmented, yielding particles of many sizes and mineral compositions
when transported by a fluid medium—air, water, or glacial ice—these particles are known collectively as sediment
three major classes of sediment: clastic (from pre-existing rocks), chemically precipitated sediment and organic sediment
Sediments and Sedimentary Rocks
sediment accumulates in more-or less horizontal layers, called strata (beds) - individual strata are separated from those below and above by surfaces called stratification planes or bedding planes
Figure 11.15, p. 410
Sediments and Sedimentary Rocks
Sediments and Sedimentary Rocks
Clastic sediment consists of inorganic rock and mineralfragments, called clasts
Figure 11.14, p. 410
chemically precipitated sediment consists of inorganicmineral compounds precipitated from a saltwatersolution or as hard parts of organisms
in the process of chemical precipitation, ions in solution combine to form solid mineral matter separate from the solution (e.g. limestone, gypsum, chert)
organic sediment consists of the tissues of plants and animals, accumulated and preserved after the death of the organism (e.g. a layer of peat in a bog or marsh)
Sediments and Sedimentary Rocks
Hydrocarbons in sedimentary rocks are compounds of carbon, hydrogen and oxygen solid fuels such as coal, liquids such as petroleum, and gas as natural gas
Sediments and Sedimentary Rocks
Figure 11.18, p. 412
metamorphic rocks are formed from preexisting rocks by intense heat and pressure, which alter rock structure and chemical composition
Heat and pressure are produced by various processes, including but not limited to tectonic activity, deep burial, and contact with magma.
shale is transformed to slate or schist, sandstone to quartzite, and limestone to marble
gneiss forms when an intrusive magma cools next to igneous or sedimentary rocks
Metamorphic Rocks
limestone marble
shale slate
sandstone quartzite
granite gneiss
basalt schist
Metamorphic Rocks
some metamorphic changes:
The Cycle of Rock Change
Figure 11.21, p. 416
the cycle of rock change describes how Earth materials are cycled andrecycled by Earth processes overgeologic time
in the surface environment, rocks weather into sediment
in the deep environment, heat and pressure transform sediment into rock that is eventually exposed at the surface