Rock geol

Earth Materials
Images 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


Igneous Rocks
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 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 Rocks
Intrusive (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 Rocks
Extrusive (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

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Volcanic Rock in N. America

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a 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

Igneous Rocks

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


Sediments and Sedimentary Rocks
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
Clastic
sediment
consists of

inorganic
rock and
mineral
fragments,
called clasts

Figure 11.14, p. 410


Sediments and Sedimentary Rocks
chemically precipitated sediment consists of inorganic
mineral compounds precipitated from a saltwater
solution 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

Figure 11.18, p. 412

Metamorphic Rocks
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
example of a schist

Figure 11.19, p. 412


Metamorphic Rocks
some metamorphic changes:

limestone

marble

shale

slate

sandstone

quartzite

granite

gneiss

basalt

schist


The Cycle of Rock Change
the cycle of rock change
describes how Earth
materials are cycled and
recycled by Earth
processes over
geologic 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
Figure 11.21, p. 416