Download Chapter 4: Rocks

 Most
buildings stones are rock-forming
minerals, such as quartz, feldspar, mice
or calcite
 Is a mixture of such minerals, rock
fragments, volcanic glass, organic
matter or other natural materials
 3 types of rocks
1. Igneous
2. Metamorphic
3. Sedimentary
 Rocks
change through processes slowly
over time
 Sedimentary rock changes by heat and
pressure to form a metamorphic rock
 Metamorphic rock melts and cools to
form an igneous
 Magma cools to form igneous rock
 Sediments are compacted into
sedimentary rock
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Over time igneous rocks can be changed into
sediments by weathering and erosion
Rock cycle processes neither create or
destroy matter (principle of conservation of
matter)
 first recognized by James Hutton in the late
18th century

Igneous rock comes from hot magma
that has been cooled
 Magma comes from deep below Earth’s
surface
 Rocks melt deep below Earth’s surface
from the pressure and temperature there
 Temperature of magma ranges from
650˚ C to 1,200 ˚ C
 Heat that melts rocks comes from the
decay of radioactive elements

Intrusive Rocks
 Are rocks that form from magma below
Earth’s surface
 Form as magma cools and mineral grains
grow together
 Are only found on the surface after layers
of rock and soil that covered them have
been removed by erosion
 It takes a long time for them too cool,
therefore mineral grains are large
1.
Extrusive Rock
 Are formed as lava cools on the Earth’s
surface
 Exposed to air and water, causing the lava
to cool quickly
 Quick cooling forms small mineral grains
2.
Igneous rocks are first classified as
intrusive or extrusive
 Further classified by the magma from
which they form
 3 forms:
1. Basaltic Rocks
 Dense dark-colored rocks
 Form from magma that is rich in iron and
magnesium and poor in silica
 Magma flows freely from volcanoes in
Hawaii
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2.
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Granitic Rocks
Light colored rocks
Lower density than basaltic rocks
Magma is thick and stiff
Contains lots of silica, lesser amounts of
iron and magnesium
Magma builds up a great deal of gas
pressure and causes violent volcanic
eruptions
Andesitic Rocks
 Mineral compositions are between
basaltic and granitic rocks
 Volcanoes that erupt andesitic magma
can be violent
3.
Rocks that have changed because of
changes in temperature and pressure and
hot fluids
 Can form from igneous, sedimentary or
other metamorphic rocks
 2 processes that form metamorphic rocks

Heat and Pressure
 Rocks under Earth’ surface are under
great pressure and temperature
 Depending on the amount of pressure
and temperature applied, one type of
rock can change into several different
metamorphic rocks
 Metamorphic rocks can come from
several kinds of parent rocks
 Ex: slate can change into phyllite then
schist, and finally gneiss
1.
2.
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Hot Fluids
Fluids, which are water mixed with
dissolved elements, react chemically with
rocks
This changes the rock’s composition
This heat from the fluid changes the rocks
during metamorphic processes
Classified according to its composition and
texture
 2 classifications
1. Foliated Rocks
 mineral grains line up in parallel layers
 Ex: Slate
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Forms from sedimentary rock shale
Arranged into layers when exposed to heat
and pressure
Water can’t pass between the layers easily
Ideal for paving around pools and patios
› Useful for roofing and tiling

Ex: Gneiss
› Forms when granite and other rocks are
changed
› Foliation shows up as alternating light and
dark bands
› Dark minerals-biotite mica
› Light minerals-quartz and feldspar
2.
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Nonfoliated Rocks
Mineral grains grow and rearrange
Do not form layers
Ex: quartzite
› Parent rock sandstone
› Composed mostly of quartz grains that
changes from a lot of pressure and heat
› Quartz grows in size and becomes
interlocking
Ex: Marble
› parent rock limestone
› Composed of calcite
› Used by artists for sculptures because it is
not as hard
75% of exposed rocks are sedimentary
 Sediments are loose materials such as rock
fragments , mineral grains and bits of shell
 Sediments come from already existing rocks
that are weathered and eroded
 Sedimentary rocks form when sediments are
pressed and cemented together or when
minerals form from solutions
 Form as layers-older layers are on the
bottom
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Sometimes forces within Earth overturn layers
of rocks and the oldest are no longer on the
bottom
Are classified by their composition and by
how they formed
 3 classifications:
1. Detrital Sedimentary Rocks
 Detritus-means wears away
 Made from the broken fragments of other
rocks
 Weathering breaks the rock into smaller
pieces
 Erosion moves sediments and causes them
to layer on top of one another
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Pressure from the top layers causes small
sediments to stick together and form a solid
rock
large sediments are cemented together by
minerals quartz and calcite
named according to the shapes and sizes of
the sediments that form them
Sizes: Clay, silt, sand, gravel (see table 2 Pg 105)
Shapes:
› Conglomerate-sediments are rounded
› Breccia-sediments have sharp angles
2. Chemical Sedimentary Rocks
 Form when dissolved minerals come out
of a solution
 Not made from pieces of pre-existing
rocks
 Ex: Limestone
› Calcium carbonate comes out of a
solution as calcite
› its crystals grow together to form
limestone
› Usually found on the bottom of lakes
or shallow seas

Ex: Rock Salt
› Water, rich in dissolved salt evaporates
and deposits halite
› Halite forms rock salt
› It is mined to use in the manufacturing of
glass, paper, soap and dairy products
› Processed
and used as table salt
Organic Sedimentary Rock
 Made of the remains of once-living things
 Ex: Most common is fossil-rich limestone
 Mostly contains remains of once-living
ocean organisms, instead of only calcite
 Shells cement together to form limestone
 Coquina-made completely of shell
fragments
 Ex: chalk-made of microscopic shells
 Ex: coal-forms when pieces of dead plants
are buried under other sediments in
swamps
3.