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

Metamorphic Rocks

example of a schist

Figure 11.19, p. 412

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