Physical Geology
The Rock Cycle
Weathering
Erosion
Soil Formation
Geohazards
Rock Cycle
• Rock- mixture of minerals, volcanic glass, organic matter, or other
materials
• Rock Cycle- model showing processes that create and change rock
1.) Sedimentary- changed by heat and pressure into metamorphic rock
2.) Metamorphic- can melt and cool to form igneous rock
3.) Igneous- rock can be broken into fragments that may later form sedimentary rock
• Conservation of matter- rock cycle never destroys elements of rocks but
merely distributes them.
• James Hutton- recognized the rock cycle in 1788 by observing Siccar Point,
Scotland
Rock Cycle
Siccar Point, Scotland
Rock Cycle
• Interactions among Earth’s water, air, land, and living things can cause rocks
to change from one type to another.
• Continuous processes that cause rocks to change their make up
• Changes in rock occur over long periods of time
Rock Cycle
Igneous Rocks
“Fire-Formed Rocks” (Ignis=fire)
• Igneous rocks- form from magma
found deep under Earth’s surface
• Form from cooling and
crystallization of magma (molten
rock beneath Earth’s surface) or
lava (on Earth’s surface)
Rock Cycle
Igneous Rocks
“Fire-Formed Rocks” (Ignis=fire)
Cooling rates influence the texture
• Quick cooling = fine grains
• Slow cooling = coarse grains
Classified by:
• Texture - Intrusive vs. Extrusive
• Chemical Composition - Mafic vs. Felsic
Rock Cycle
Igneous Rocks
• Intrusive- (interior) magma
trapped below the surface
forms large-grained rock
when it cools
• Extrusive- (exterior) magma
cooling quickly at or near
Earth’s surface forms smallgrained rock, or no crystals
(glass or porous texture)
Rock Cycle
Felsic
Igneous Rocks
Rock Composition
• Dominated by silicon and aluminum (SiAl)
• Usually light in color
• Characteristic of continental crust
• Forms a stiff (viscous) lava or magma
• Rock types include: granite & rhyolite
Intermediate
• Intermediate in composition between felsic and mafic
• Rock types include: Andesite & Diorite
Rock Cycle
Igneous Rocks
Rock Composition
Mafic (or basaltic)
• Usually dark in color (dark gray to black)
• Forms a runny (low viscosity) lava
• Characteristic of Earth's oceanic crust, Hawaiian volcanoes
• Rock types include: basalt, gabbro, diabase
Ultramafic
• Rarely observed on the Earth's surface
• Believed to be major constituent of Earth's mantle
• Rock types include: peridotite
Rock Cycle
Igneous Rocks
Magma Type or Chemical Composition
• Mafic• HOTTER
• FAST moving
• THIN fluid
• HIGH metal
• DARK color
• MORE dense
• Felsic
• COOLER
• SLOW moving
• THICK fluid
• HIGH silica
• LIGHT color
• LESS dense
Rock Cycle
Igneous Rocks
Magma Type
• Basaltic (mafic)- extrusive
• Dark-colored and dense
• Contain iron and magnesium but very
little silica
• Basaltic lava flows freely from a volcano
• Granitic (felsic)- intrusive
• Contain more silica and less iron and
magnesium
• Granitic magma is thick and stiff
• Andesitic- extrusive
• More balanced composition of minerals
and density than basaltic or granitic
Rock Cycle
Igneous Rocks
Rock Texture
Coarse grain (visible) – forms due to slow cooling of magma
underground, composed of large crystals (e.g. granite, diorite,
gabbro)
Fine grain – forms due to rapid cooling of lava at Earth's
surface, composed of tiny crystals (e.g. basalt, rhyolite,
andesite)
Porphyritic- Mixture of grain sizes caused by mixed cooling
history; slow cooling first, followed by a period of somewhat
faster cooling.
Rock Cycle
Igneous Rocks
Rock Texture
Glassy – forms as lava cools very rapidly at Earth's surface, in a
matter of seconds or a few minutes. (e.g. obsidian)
Pyroclastic – forms as an explosive volcanic eruption mixes
fragments of the volcano with hot ash in the atmosphere. (e.g.
tuff)
Vesicular – holes or cavities as a result of gas expansion
(bubbles) that occurs during volcanic eruption (e.g. scoria,
basalt)
Frothy – forms as gas-charged lava cools very rapidly at Earth's
surface. (e.g. pumice)
Rock Cycle
Igneous Rocks
Rock Cycle
Igneous Rocks
A batholith is a great mass of
igneous intrusive rock that
forms from cooled magma
deep in the Earth's crust.
They are formed when
multiple plutons converge to
form a huge expanse of
granite rock.
Sierra Nevada Batholith in
Yosemite National Park
Rock Cycle
Igneous Rocks
A vein is at the end of the
crystallization process when
mineral rich fluid fills voids and
cracks
- Forms gold or other rare minerals
- Pegmatites: extremely large
grained minerals (gem stones)
- Kimberlites: found in rare
ultramafic rock, extremely deep
and under high pressure
(diamonds)
Rock Cycle
Metamorphic Rocks
Metamorphic Rock- changed by temperature, pressure,
and hot fluids
Rock Cycle
Metamorphic Rocks
1.) Heat and pressure result from one layer of rock on
top of another layer.
- temperature and pressure are great enough to
melt rock, forming magma
- pressure alone flattens mineral grains in rocks without
melting them
- as pressure and temperature continue to increase
over time, one type of rock can change into several
different metamorphic rocks
Rock Cycle
Metamorphic Rocks
2.) Hot, water-rich
fluids can move
through rock,
chemically changing it
Rock Cycle
Metamorphic Rocks
Classification of metamorphic rocks- by composition
and texture
1.) Foliated texture- mineral grains flatten and line
up in parallel layers or bands
2.) Non-foliated- mineral grains grow and
rearrange but do not form layers
Animation
Rock Cycle
Sedimentary Rocks
Mostly found on the exposed surface of Earth
• Rock fragments, mineral grains, and bits of plants and
animal remains moved by wind, water, ice or gravity are
called sediments
• Sedimentary rocks form in layers
Rock Cycle
Sedimentary Rocks
- Classified by what they were made of and how they were formed
- Detrital sedimentary rocks- made from broken fragments of other rocks
1.) compaction- layers of small sediments stick together because of
pressure
2.) cementation- water and other minerals move through open
spaces between larger sediments, gluing them together
3.) granular texture
4.) named according to size and shape of sediments
a.) size can be large like gravel or small like clay
b.) well-rounded or have sharp angles
Rock Cycle
Sedimentary Rocks
- Chemical sedimentary rocks- non-clastic rocks formed
when dissolved minerals came out of solution
1.) Limestone forms from calcite, which was calcium carbonate in solution
2.) Rock salt forms from halite, which was salt in solution
- Organic sedimentary rocks- made from remains of onceliving plants or animals
1.) Chalk- made of microscopic calcite-shell remains of animals
2.) Coal- made of plant remains, chemically changed by microorganisms and compacts
over millions of years
Process of Creating a Sedimentary Rock
Step 1.) Weathering
Step 2.) Erosion-movement of surface materials from one place to another.
Step 3.) Deposition- sediments are laid down on the ground or sink to the
bottoms of bodies of water.
Step 4) Burial-sediments layer, pressure and temperature increase; results in
bedding, or horizontal layering.
Step 5) Lithification- Lithify comes from the Greek word lithos, which
means “stone.”
- physical and chemical process by which sediments are transformed into
sedimentary rocks.
- involves “compaction” and “cementation.”
Lithification
Sediment
Rock
REVIEW- Major Rock Groups
• Igneous
• Formed from a melt (molten rock)
• Plutonic (intrusive):slow cooling and crystallization
• Volcanic (extrusion): quick cooling at the surface
• Sedimentary
• Formed at the Earth’s surface
• Clastic/Detrital (Mineral Fragments or grains, clays)
• Chemical (crystalline chemical/biochemical precipitates)
• Metamorphic
• Changed by pressure, temperature and fluids.
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MAGMA
IGNEOUS
Crystallization
MAGMA
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IGNEOUS
Plutonic
Crystallization
MAGMA
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Volcanic
IGNEOUS
Plutonic
Crystallization
MAGMA
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Weathering
Volcanic
IGNEOUS
Plutonic
Crystallization
Uplift
MAGMA
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Weathering
SEDIMENT
Volcanic
IGNEOUS
Plutonic
Crystallization
Uplift
MAGMA
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Weathering
SEDIMENT
Erosion
Transport
Deposition
Volcanic
SEDIMENTARY
IGNEOUS
Plutonic
Crystallization
Uplift
MAGMA
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Weathering
SEDIMENT
Erosion
Transport
Deposition
Volcanic
SEDIMENTARY
IGNEOUS
Plutonic
Crystallization
Uplift
MAGMA
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Weathering
SEDIMENT
Erosion
Transport
Deposition
Volcanic
SEDIMENTARY
IGNEOUS
Plutonic
Increased P&T
METAMORPHIC
Crystallization
Burial
Uplift
MAGMA
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Weathering
SEDIMENT
Erosion
Transport
Volcanic
Can you see
IGNEOUS
any shortcuts?
Deposition
SEDIMENTARY
Plutonic
Increased P&T
METAMORPHIC
Crystallization
Melting
Burial
Uplift
MAGMA
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Weathering
SEDIMENT
Erosion
Transport
Deposition
Volcanic
SEDIMENTARY
IGNEOUS
Plutonic
Increased P&T
METAMORPHIC
Crystallization
Melting
Burial
Uplift
MAGMA
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Forms of Energy that Drive Cycle
1) Heat-creates magma, causes
metamorphism
2) Mechanical (gravitational potential)
energy-ability of sediments to move
downhill, plate motion due to gravity,
metamorphism occurs as a result of plate
motion