Download Rocks chapter 3

 What
is a rock?
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◦ Common rocks: rock is a mixture of
minerals, rock fragments, volcanic glass,
organic matter and other natural materials
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Rock cycle illustrates the processes that
create and change rocks
Rock interchange between igneous,
sedimentary and metamorphic rock
depending how they form , the process it
takes to form new rock and may take millions
of years to form
When matter weathers it is not lost but
arranged in perhaps different forms
Formation of Igneous Rock: Hot magma cools
and solidifies to form igneous rock
 Magma: the decay of radioactive elements
deep in earth interior and intense pressure
cause rocks below 150 km to melt. That
melted rock is called magma
 Magma is less dense and rises to surface.
When it reaches the surface it is called lava
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 Rock
that cools underneath the surface is
intrusive rock
 Cooling is slower and slower than rock
that reaches the surface
 The slower rock cools the larger the
crystal form (coarse grained)
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Magma cools at the surface and is called
extrusive rock
Crystals do not have time to form generally
(fine grained)
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Pumice, obsidian and scoria are examples of
volcanic glass
These cool so fast that few or no mineral
grains form
Gas is trapped in mineral leading to pockets
of gas trapped in mineral
Basaltic Rock: rock rich in iron, dark, dense,
poor in silica(SiO2) (basalt is an example)
 Granitic rock; rich in silica, light colored,
lower density: builds up pressure before
released. Usually cools before it reaches the
surface (granite is example)
 Andesitic Rock: composition between
basaltic and granitic rock (Cascade Mt are
example)
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 Metamorphic
rock is changed rock
caused by intense pressure and
temperature deep under earths surface
 Can form from a parent material of
igneous or sedimentary rock or
metamorphic rock
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Shale can change to slate
Slate into schist, and eventually to gneiss
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Foliated rocks: when mineral grains
line up in parallel layers, it is said to
have metamorphic foliated texture
◦ Slate: watertight metamorphic rock
caused by pressure is used in pools and
roofs
◦ Gneiss: forms when granite is put under
intense pressure and give layers of light
and dark areas
Metamorphic rock where layering doesn’t
form but form rearrange layers are nonfoliated
rocks
 Sandstone is sedimentary rock that when
heated and under lots of pressure form
quartzite with interlocking quartz in between
 Marble: composed of mineral calcite
(limestone), that has under gone intense
pressure and temperature
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Formation of Sedimentary Rock
◦ 75 % of rocks exposed at the surface are
sedimentary rocks
◦ Sediments are loose materials ie rock
fragments, minerals grains, bits of shell
moved by wind water, ice, or gravity
◦ Sedimentary rocks forms when sediments
are pressed and cemented together or when
minerals form from solution
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Rocks that are deposited in layers usually
hold the rocks at the bottom of layers are
older and younger rocks rest on top
On occasions, the layers get messed up and
the age of the rocks don’t hold true to the
layers
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Classified by being either detrital, chemical or
organic
Detrital: sedimentary rock made from the broken
fragments of other rock which are compacted and
cemented together
Rock first must be broken down or weathered and then
moved to another location by erosion
Compaction of smaller particles can stick together to
form solid rock under pressure
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Cementation: larger sediment (pebbles and sand)
with only pressure can’t bind together, but rather
need cementation to hold rock together
Water mixed with dissolved material acts as a cement
to hold larger particles together
Shape and size of sediment are given names
Conglomerate (rounded pieces of pebbles cemented
together
Breccia are sharp jagged pieces cemented together
Can be chunks of minerals, (quartz,feldspar)
pieces of gneiss, granite, limestone
◦ The cement usually made up of quartz or
calcite
 Sandstone is formed from smaller particles
 Sand size particles usually quartz and feldspar
 Siltstone: similar to sandstone except
granules are smaller
 Shale: particles made from clay sized particles
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These rocks are not made from pre-existing
rock
 These rocks form when dissolved minerals
come out of solution
 When evaporation takes place in a solution of
minerals, they will drop out of solution
 Gypsum: rock from New Mexico
 Limestone: Calcium carbonate carried to
ocean in solution and comes out of solution in
form of calcite (usually deposited in shallow
lakes)
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Rock salt: halite forms from salt (NaCl) that
evaporates out of solution and forms cubic
crystals
Rock forms from the once living remains
 Most common is fossil-rich limestone
 Formed from once living ocean organisms
instead of just calcite deposits
 Shells of marine organism are made of CaCO3
 that eventually becomes calcite where they are
cemented together
 Coquina : rock made of shell fragments
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Chalk: calcite-shell remains of once living
ocean organisms
 Coal: dead plants are buried under other
sediment in swamps
 Plants become chemical changed by organisms
 United States has a lot of coal produced in
Carboniferous period (290-360 million ya)
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Rock cycle has no beginning or end
 Rocks formed can be uplifted, weathered,
eroded, buried, cemented, melted, more
pressure, uplift continuously
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