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Rocks
How Geologists Classify Rocks
► When
studying a
rock sample,
geologists observe
the rock’s color and
texture and
determine its mineral
composition.
► Geologists can then
identify a rock’s
origin, or where and
how it formed.
Texture
► Most
rocks are made
up of particles of
minerals or other
rocks, called grains.
► A rock’s texture is the
size, shape, and
pattern of the rock’s
grains.
► Some rocks are
smooth and glassy,
others are rough or
chalky.
Grains
► Texture
due to the
grains can vary
depending on the
grain:
► Size (fine/coarse)
► Shape
(rounded/jagged)
► Pattern
(Banded/Nonbanded)
► Visible/Invisible
Three Major Groups of Rocks
Igneous Rock
► Any
rock that forms from
magma or lava.
► Extrusive rock is igneous
rock formed from lava
that erupted onto Earth’s
surface.
► Example: Basalt
► Intrusive rock is igneous
rock that formed when
magma hardened beneath
the Earth’s surface.
► Example: Granite
Igneous Rock
► Igneous
rocks are
classified according to
their origin, texture,
and mineral
composition.
► Origin:
Intrusive/Extrusive
► Texture: fine/coarse
grained, porphyritic,
etc…
► Mineral Composition:
silica content
Sedimentary Rocks
► Sedimentary
rocks
form from particles
(sediments)
deposited by water
and wind.
► Sediment is small,
solid pieces of
material that come
from rocks or living
things.
Sedimentary Rock Cycle
► Sediment
undergoes the
following process
that will change it
into sedimentary
rock.
► 1) Erosion
► 2) Deposition
► 3) Compaction
► 4) Cementation
Erosion and
Deposition
► Erosion
occurs when
running water or wind
loosens and carries
away fragments of
rock.
► Deposition is when
sediment settles out
of the wind or water
carrying it.
► After the sediments
have been deposited,
they begin to compact.
Compaction and Cementation
► Compaction
is the
process of pressing
the sediments
together.
► While compaction is
taking place, minerals
dissolve and seep in
between the spaces.
► Cementation occurs
when the minerals
crystallize and “glue”
the sediment
together.
Types of Sedimentary Rocks
► There
are three major
groups of sedimentary
rocks: Clastic, Organic,
and Chemical rocks.
► Clastic: Rock
fragments squeezed
together.
► Organic: Plant and
animal remains.
► Chemical: Minerals
dissolved in a solution
crystallize.
Clastic Rocks:
Shale: particles of clay
Sandstone: sand on
beaches.
Conglomerate: rock
fragments of different
sizes.
► Organic Rocks:
Coal: swamp plant remains
Limestone: made from
shells.
► Chemical Rocks:
Rock Salt: mineral
evaporation.
►
Rock Examples
Metamorphic Rocks
►
►
►
Metamorphic comes
from the Greek word
meta that mean
“change” and
morphosis that means
“form”
HEAT AND PRESSURE
deep beneath the
Earth’s surface can
change ANY rock into
metamorphic rock.
Forces can push rock
back toward the heat of
the mantle and change
rock to metamorphic
rock.
Classifying Metamorphic Rocks
► Geologists
classify
metamorphic rocks by
the arrangement of the
grains that make up
the rocks.
► Grains arranged in
parallel layers or bands
are said to be foliated.
► Some metamorphic
rocks are nonfoliated
and the grains are
arranged randomly.