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ROCKS
By Gina Wike
ROCKS
• A rock is defined as a mixture of minerals,
mineraloids, glass, or organic matter
Rock-forming Minerals
1. Quartz- one of the 2 most abundant
minerals
2. Feldspar- one of the 2 most abundant
minerals
3. Hornblende
4. Mica
3 TYPES OF ROCKS
• Igneous
• Metamorphic
• Sedimentary
THE ROCK CYCLE
• The rock cycle shows that any rock,
whether it be igneous, metamorphic, or
sedimentary, can change into another type
of rock depending upon the processes that
change them
Rock-changing Processes
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Weathering
Erosion
Compaction
Cementation
Melting
Cooling
Rock Changing Processes
SEDIMENTARY
Weathering
Erosion
Compaction
Cementation
The compaction and cementation of sediments
form sedimentary rocks. Weathering of rock
forms sediments. Erosion then moves the
sediments.
Rock Changing Processes
METAMORPHIC
Heat
Pressure
Heat and pressure change rocks into metamorphic
rocks. Even metamorphic rocks can change into
different metamorphic rocks when heat and
pressure are added.
Rock Changing Processes
IGNEOUS
Melting
Cooling
The cooling of melted rock (magma or lava)
forms igneous rock.
Rocks that form from magma or
lava
Igneous Rocks
• Igneous rocks form when molten material
(magma & lava) cools
• Magma is less dense than the surrounding
rock, so it rises.
• When magma cools slowly, there are
LARGE crystals or mineral grains.
• When magma cools quickly, the grains or
crystals are small- even microscopic.
IGNEOUS ROCKS
• Igneous rocks can be classified by where
they form (LOCATION)
• Intrusive Igneous
• Extrusive Igneous
Intrusive Igneous Rocks
• Form below the Earth’s surface; inside the
Earth
• Crystals are large because the magma
cools slowly
• Coarse-grained
• Found at the earth’s surface only when
forces inside the Earth push them up or
when weathering & erosion expose them
INTRUSIVE IGNEOUS
• Example: Granite is an intrusive igneous
rock
EXTRUSIVE IGNEOUS ROCK
• Found at the earth’s surface
• Crystals are small because the lava cools
quickly
• Fine-grained or small-grained
• Examples: Obsidian & pumice
OBSIDIAN
• Obsidian looks like black glass.
Pumice
• Pumice floats in water because it is less
dense than the water.
• Pumice has holes in it from where gas
escapes as the molten material cools.
• It is used in hand cleansers because of its
abrasive quality.
IGNEOUS ROCKS
• Igneous rock can be classified by the type
of minerals in the magma or lava
• Basaltic
• Andesitic
• Granitic
BASALTIC ROCKS
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Made of basaltic magma or lava
Rich in iron and magnesium
Dark-colored
Heavy
Dense
GRANITIC
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Made of granitic magma or lava
Rich in silicon & oxygen
Light-colored
Lower in density
ANDESITIC
• Composition between that of basaltic and
granitic
IGNEOUS ROCKS
• Igneous rocks are the most abundant on
Earth
• Basalt is the most common extrusive
igneous rock.
METAMORPHIC ROCKS
Form from heat & pressure
METAMORPHIC ROCK
• Metamorphic rocks are formed when heat
and pressure are added to sedimentary,
igneous, and even metamorphic rocks.
• One type of rock can change into several
different rocks, depending upon the
amount of heat and pressure applied.
METAMORPHIC ROCKS
• Metamorphic rocks have 2 classifications:
Foliated
&
Nonfoliated
FOLIATED
• This is when mineral grains flatten and line
up in parallel bands
• These rocks will separate easily between
the layers
• Examples: Gneiss & Slate
• Folded foliation pictured below:
Slate
• Slate forms when heat and pressure are
applied to shale.
• Slate is used in roofing because it
separates easily into layers.
NONFOLIATED
• No banding or parallel layers
• Mineral grains change, grow, or rearrange
• Nonfoliated rocks fracture into pieces of
random size.
• Example: marble
METAMORPHIC ROCKS
Original
Rock
Rock Type of Original
Rock
Metamorphic
Rock
Formed
Limestone
Sedimentary
Marble
Sandstone
Sedimentary
Quartzite
Shale
Sedimentary
Slate
Granite
Igneous
Gneiss
SEDIMENTARY ROCKS
Form from compaction and
cementation of sediments
SEDIMENTARY ROCKS
• 75% of rocks at the Earth’s surface are
sedimentary rocks
• Sedimentary rocks form when sediments
become pressed or cemented together.
• Sediments are loose material such as rock
fragments, minerals, and bits of plant and animal
remains.
• Weathering is the process that breaks rock into
smaller pieces.
• Erosion is the movement of sediments.
SEDIMENTARY ROCKS
• If sediments are small, they can be
compacted or packed together to form
sedimentary rocks.
• This process is compaction.
• If sediments are large, they must be glued
or cemented together. Minerals mix with
water to form natural cement or glue.
• This process is cementation.
SEDIMENTARY ROCKS
• Sediment sizes: (smallest to largest)
clay- smallest
silt
sand
gravel- largest
SEDIMENTARY ROCKS
• Sedimentary rocks form as layers, or
strata.
• Sediments are put down horizontally.
• The oldest layers are on the bottom.
SEDIMENTARY ROCK
• Classification of rock layers
Clastic
Chemical
Organic
CLASTIC
• Named by shape & size of sediment
• Large sediments:
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1. Conglomerate
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2. Breccia
• Small sediments:
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1. Shale
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2. Sandstone
CHEMICAL
• Form when sediments precipitate out of a
solution
• Examples:
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1. Rock salt
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2. Limestone
ORGANIC
• Form from once-living things
• Examples:
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1. Fossil-rich limestone
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2. Coquina
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3. Chalk
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4. Coal