CHAPTER 1 — INTRODUCTION
Physical Geology vs. Historical Geology
Physical Geology — focuses on Earth's internal and external processes.
Historical Geology — focuses on the sequence of events that happened throughout Earth's history.
"Rocks are Events" — rocks can record evidence of events that happened in Earth's past.
Scientific Inquiry
The goal of scientific inquiry is to find patterns and use them to make predictions.
Science assumes that the natural world is understandable.
A good scientific explanation should explain all available observations, while the simplest idea is usually the best.
What makes a good hypothesis?
A good hypothesis should:
Explain all available observations.Be simple.
Uniformitarianism
Uniformitarianism — the idea that the processes we observe today can help us understand Earth's past.
"THE PRESENT IS THE KEY TO THE PAST"
Scientific Method
Know the basic sequence:
Data → Hypothesis → Test → Theory
Data — observations and information collected by scientists.
Hypothesis — an initial idea or prediction that can be tested against observations.
Test — an experiment or other method used to test the hypothesis.
Theory — an idea that has been rigorously tested and supported over many years, leading to general agreement among scientists.
Glacial vs. Wind vs. Water-Laid Sediments
Know that glaciers, wind, and water can transport and deposit sediment.
The important distinction to recognize is the environment/process that deposited the sediment:
Glacial → deposited by glaciers/ice.Wind → deposited by wind.Water-laid → deposited by water.
Earth's 4 Spheres
Earth has four major interconnected spheres:
1. Geosphere
Geosphere → the solid Earth, including rocks and soil.
2. Biosphere
Biosphere → organic life.
3. Atmosphere
Atmosphere → the gases surrounding Earth.
4. Hydrosphere
Hydrosphere → all water and ice, including surface and underground water.
Two-way exchanges
The four spheres are interconnected, meaning materials and energy can move between them in two-way exchanges.
EOS — Earth Observing System
EOS — Earth Observing System
→ Satellites monitoring Earth's systems.
Three Interconnected Cycles
Know these three:
Hydrologic CycleRock CycleTectonic Cycle
They are interconnected cycles that operate within Earth's systems.
EARTH IN SPACE — THE SOLAR SYSTEM
4 Terrestrial vs. 4 Gas Giant Planets
Terrestrial planets
The four terrestrial planets are:
Mercury, Venus, Earth, Mars
They are the rocky planets.
Gas giant planets
The four gas giants are:
Jupiter, Saturn, Uranus, Neptune
Nebular Hypothesis
Nebular Hypothesis → explains the formation of the solar system.
Planetary Accretion
Planetary accretion → material comes together to form planets.
Chemical Differentiation
Chemical differentiation produced Earth's major layers:
Core → Mantle → Crust
Core
IronInner core = solidOuter core = liquid
Mantle
Iron- and magnesium-rich rocks
Crust
Silicon- and oxygen-rich rocks
The crust has two types:
Oceanic crustContinental crust
What Makes Earth Unique?
The review sheet specifically identifies the:
Biosphere
Earth has a biosphere that supports life.
CHAPTER 2 — MINERALS
Elements
An element is a basic type of matter made of atoms of the same element.
Atoms
Atoms contain:
Protons → positive charge
Neutrons → no charge
Electrons → negative charge
Atomic Number vs. Mass Number
Atomic number → number of protons.
Mass number → number of protons + neutrons.
Isotopes
Isotopes → atoms of the same element with different numbers of neutrons.
Atoms vs. Ions
Atom → electrically neutral when it has equal numbers of protons and electrons.
Ion → an atom that has gained or lost electrons and therefore has a charge.
Ionic vs. Covalent Bonds
Ionic bond → involves attraction between oppositely charged ions.
Covalent bond → atoms share electrons.
For minerals, remember that the silicon-oxygen bonds in the silicate structure are covalent and very strong.
Octet Rule
Octet rule → atoms tend to gain, lose, or share electrons to obtain a stable outer electron arrangement.
Atomic Substitution
Atomic substitution → one ion replaces another ion of similar size and charge.
Olivine
In olivine:
Mg²⁺ and Fe²⁺ can substitute for each other.
Why?
Because they have:
Similar sizeThe same charge
Olivine can therefore have:
Fe₂SiO₄
Mg₂SiO₄
or an intermediate mixture:
(Mg, Fe)₂SiO₄
Elemental Abundances in Continental Crust
Know the important elements listed on your review sheet:
Silicon (Si)
Oxygen (O)
The review sheet specifically wants you to know the abundance of Si and O in the continental crust.
Silicon-Oxygen Tetrahedron
The basic building block of silicate minerals is the:
Silicon-Oxygen Tetrahedron
Formula:
(SiO₄)⁴⁻
It contains:
1 Si4 O
So remember:
SiO₄ = 1 silicon + 4 oxygen
It is a complex ion because it contains more than one element.
Complex vs. Simple Ions
Simple ion → contains one element.
Complex ion → contains more than one element.
Example:
O²⁻ → simple ion
(SiO₄)⁴⁻ → complex ion
Mineral Types and Families
Know these mineral families from the review sheet:
Silicates
Contain silicon and oxygen.
SiO₄
They are the most abundant mineral group.
Carbonates
Contain the carbonate ion:
CO₃
Sulfides
Associated with sulfur (S).
Evaporites
The review sheet gives:
NaCl — halite
as the example to know.
CHAPTER 6 — IGNEOUS ROCKS
Melting Rocks
Rock is a mixture of minerals.
Because different minerals have different melting temperatures, rocks melt over a range of temperatures.
The review sheet gives approximately:
800–1,200°C
Geothermal Gradient
Geothermal gradient → the rate of temperature increase with depth.
The rate is approximately:
Ocean floor → 13°C/km
Continental crust → 6.7°C/km
The geothermal gradient is therefore about twice as rapid beneath the ocean floor as beneath continental crust.
Why Rocks in the Mantle Stay Solid
The temperature in the upper mantle can be above the melting point of rocks at Earth's surface.
However:
Pressure increases with depth → melting point increases
Therefore, the rocks can remain solid because of the increased pressure.
Pressure-Temperature Relationship
Remember:
Pressure ↑ → Melting point ↑
Water → Melting point ↓
These are two extremely important relationships for the test.
Fractional Melting vs. Fractional Crystallization
Fractional Melting
Rock contains many different minerals, and each mineral melts at a different temperature.
Therefore, only part of the rock may melt.
Fractional melt → only a fraction of the rock melts.
Fractionation → magma separates from the remaining solid material.
Basic idea:
Rock → partial melting → magma + solid
Fractional Crystallization
This is essentially the reverse of melting.
Crystals form and then separate from the magma.
Basic idea:
Magma → crystals separate → rock + remaining magma
The resulting rock and magma have different compositions from the original magma.
Three Factors Affecting Magmas and Lavas
Know these three:
CompositionTemperatureViscosity
Silica and Viscosity
High silica
High silica → high viscosity → thick
High temperature
High temperature → low viscosity → thin
Remember:
Silica ↑ → Viscosity ↑
Temperature ↑ → Viscosity ↓
Cooling Rate
Fast Cooling
Fast cooling → small crystals
Extrusive → volcanic
Slow Cooling
Slow cooling → large crystals
Intrusive → plutonic
Easy way to remember:
Fast = Small
Slow = Large
Porphyritic Texture
Porphyritic texture has:
Coarse crystals surrounded by fine crystals.
It forms through two cooling rates:
Slow → Fast
The magma:
Starts deep underground.Cools slowly, allowing large crystals to form.Erupts.The remaining magma cools quickly.Fine crystals form around the large crystals.
So:
Porphyritic = starts deep → slow cooling → erupts → fast cooling
FELSIC vs. MAFIC
FELSIC
High silica
Lots of quartz and feldsparLow Fe and MgAssociated with continental crust
Remember:
FELSIC = high silica + continental
MAFIC
Low silica
Ferromagnesian mineralsHigh Fe and MgAssociated with oceanic crust
Remember:
MAFIC = Fe/Mg + oceanic
Igneous Rock Bodies
Know these four:
Batholith
Large intrusive igneous body.
Example: Sierra Nevada Batholith
Stock
Intrusive igneous body smaller than a batholith.
Dike
Igneous body that cuts across existing rock.
Sill
Igneous body that forms parallel to existing rock.
Palisades
Palisades → Mafic sill
The review sheet connects the Palisades Sill with:
The breakup of Pangaea.
⭐ TEST MEMORY SHEET
If you want the absolute shortest version to memorize:
Physical Geology → internal + external processes
Historical Geology → sequence of events
Uniformitarianism → present is key to past
Scientific Method → Data → Hypothesis → Test → Theory
4 Spheres → Geo, Bio, Atmo, Hydro
EOS → satellites
3 Cycles → Hydrologic, Rock, Tectonic
Terrestrial → Mercury, Venus, Earth, Mars
Gas Giants → Jupiter, Saturn, Uranus, Neptune
Nebular Hypothesis → solar system
Accretion → planets form from accumulating material
Differentiation → Core, Mantle, Crust
Core → iron; inner solid, outer liquid
Mantle → Fe + Mg
Crust → Si + O
Earth unique → Biosphere
Atomic # → protons
Mass # → protons + neutrons
Isotopes → different neutrons
Ion → charged atom
Atomic substitution → similar size + charge
Olivine → Mg²⁺ ↔ Fe²⁺
Silicate → Si + O
Tetrahedron → (SiO₄)⁴⁻
Complex ion → >1 element
Rock → mixture of minerals
Pressure → melting point ↑
Water → melting point ↓
Geothermal gradient → temperature ↑ with depth
Fractional melting → some melts, some stays solid
Fractional crystallization → crystals separate from magma
High silica → thick/high viscosity
High temperature → thin/low viscosity
Fast cooling → small/extrusive/volcanic
Slow cooling → large/intrusive/plutonic
Porphyritic → slow → fast
Felsic → high silica, quartz/feldspar, continental
Mafic → low silica, Fe/Mg, oceanic
Batholith → Stock → Dike → Sill
Sierra Nevada → Batholith
Palisades → Mafic Sill → Pangaea breakup
CHAPTER 1 — INTRODUCTION
Physical Geology vs. Historical Geology
Physical Geology — focuses on Earth's internal and external processes.
Historical Geology — focuses on the sequence of events that happened throughout Earth's history.
"Rocks are Events" — rocks can record evidence of events that happened in Earth's past.
Scientific Inquiry
The goal of scientific inquiry is to find patterns and use them to make predictions.
Science assumes that the natural world is understandable.
A good scientific explanation should explain all available observations, while the simplest idea is usually the best.
What makes a good hypothesis?
A good hypothesis should:
Explain all available observations.Be simple.
Uniformitarianism
Uniformitarianism — the idea that the processes we observe today can help us understand Earth's past.
"THE PRESENT IS THE KEY TO THE PAST"
Scientific Method
Know the basic sequence:
Data → Hypothesis → Test → Theory
Data — observations and information collected by scientists.
Hypothesis — an initial idea or prediction that can be tested against observations.
Test — an experiment or other method used to test the hypothesis.
Theory — an idea that has been rigorously tested and supported over many years, leading to general agreement among scientists.
Glacial vs. Wind vs. Water-Laid Sediments
Know that glaciers, wind, and water can transport and deposit sediment.
The important distinction to recognize is the environment/process that deposited the sediment:
Glacial → deposited by glaciers/ice.Wind → deposited by wind.Water-laid → deposited by water.
Earth's 4 Spheres
Earth has four major interconnected spheres:
1. Geosphere
Geosphere → the solid Earth, including rocks and soil.
2. Biosphere
Biosphere → organic life.
3. Atmosphere
Atmosphere → the gases surrounding Earth.
4. Hydrosphere
Hydrosphere → all water and ice, including surface and underground water.
Two-way exchanges
The four spheres are interconnected, meaning materials and energy can move between them in two-way exchanges.
EOS — Earth Observing System
EOS — Earth Observing System
→ Satellites monitoring Earth's systems.
Three Interconnected Cycles
Know these three:
Hydrologic CycleRock CycleTectonic Cycle
They are interconnected cycles that operate within Earth's systems.
EARTH IN SPACE — THE SOLAR SYSTEM
4 Terrestrial vs. 4 Gas Giant Planets
Terrestrial planets
The four terrestrial planets are:
Mercury, Venus, Earth, Mars
They are the rocky planets.
Gas giant planets
The four gas giants are:
Jupiter, Saturn, Uranus, Neptune
Nebular Hypothesis
Nebular Hypothesis → explains the formation of the solar system.
Planetary Accretion
Planetary accretion → material comes together to form planets.
Chemical Differentiation
Chemical differentiation produced Earth's major layers:
Core → Mantle → Crust
Core
IronInner core = solidOuter core = liquid
Mantle
Iron- and magnesium-rich rocks
Crust
Silicon- and oxygen-rich rocks
The crust has two types:
Oceanic crustContinental crust
What Makes Earth Unique?
The review sheet specifically identifies the:
Biosphere
Earth has a biosphere that supports life.
CHAPTER 2 — MINERALS
Elements
An element is a basic type of matter made of atoms of the same element.
Atoms
Atoms contain:
Protons → positive charge
Neutrons → no charge
Electrons → negative charge
Atomic Number vs. Mass Number
Atomic number → number of protons.
Mass number → number of protons + neutrons.
Isotopes
Isotopes → atoms of the same element with different numbers of neutrons.
Atoms vs. Ions
Atom → electrically neutral when it has equal numbers of protons and electrons.
Ion → an atom that has gained or lost electrons and therefore has a charge.
Ionic vs. Covalent Bonds
Ionic bond → involves attraction between oppositely charged ions.
Covalent bond → atoms share electrons.
For minerals, remember that the silicon-oxygen bonds in the silicate structure are covalent and very strong.
Octet Rule
Octet rule → atoms tend to gain, lose, or share electrons to obtain a stable outer electron arrangement.
Atomic Substitution
Atomic substitution → one ion replaces another ion of similar size and charge.
Olivine
In olivine:
Mg²⁺ and Fe²⁺ can substitute for each other.
Why?
Because they have:
Similar sizeThe same charge
Olivine can therefore have:
Fe₂SiO₄
Mg₂SiO₄
or an intermediate mixture:
(Mg, Fe)₂SiO₄
Elemental Abundances in Continental Crust
Know the important elements listed on your review sheet:
Silicon (Si)
Oxygen (O)
The review sheet specifically wants you to know the abundance of Si and O in the continental crust.
Silicon-Oxygen Tetrahedron
The basic building block of silicate minerals is the:
Silicon-Oxygen Tetrahedron
Formula:
(SiO₄)⁴⁻
It contains:
1 Si4 O
So remember:
SiO₄ = 1 silicon + 4 oxygen
It is a complex ion because it contains more than one element.
Complex vs. Simple Ions
Simple ion → contains one element.
Complex ion → contains more than one element.
Example:
O²⁻ → simple ion
(SiO₄)⁴⁻ → complex ion
Mineral Types and Families
Know these mineral families from the review sheet:
Silicates
Contain silicon and oxygen.
SiO₄
They are the most abundant mineral group.
Carbonates
Contain the carbonate ion:
CO₃
Sulfides
Associated with sulfur (S).
Evaporites
The review sheet gives:
NaCl — halite
as the example to know.
CHAPTER 6 — IGNEOUS ROCKS
Melting Rocks
Rock is a mixture of minerals.
Because different minerals have different melting temperatures, rocks melt over a range of temperatures.
The review sheet gives approximately:
800–1,200°C
Geothermal Gradient
Geothermal gradient → the rate of temperature increase with depth.
The rate is approximately:
Ocean floor → 13°C/km
Continental crust → 6.7°C/km
The geothermal gradient is therefore about twice as rapid beneath the ocean floor as beneath continental crust.
Why Rocks in the Mantle Stay Solid
The temperature in the upper mantle can be above the melting point of rocks at Earth's surface.
However:
Pressure increases with depth → melting point increases
Therefore, the rocks can remain solid because of the increased pressure.
Pressure-Temperature Relationship
Remember:
Pressure ↑ → Melting point ↑
Water → Melting point ↓
These are two extremely important relationships for the test.
Fractional Melting vs. Fractional Crystallization
Fractional Melting
Rock contains many different minerals, and each mineral melts at a different temperature.
Therefore, only part of the rock may melt.
Fractional melt → only a fraction of the rock melts.
Fractionation → magma separates from the remaining solid material.
Basic idea:
Rock → partial melting → magma + solid
Fractional Crystallization
This is essentially the reverse of melting.
Crystals form and then separate from the magma.
Basic idea:
Magma → crystals separate → rock + remaining magma
The resulting rock and magma have different compositions from the original magma.
Three Factors Affecting Magmas and Lavas
Know these three:
CompositionTemperatureViscosity
Silica and Viscosity
High silica
High silica → high viscosity → thick
High temperature
High temperature → low viscosity → thin
Remember:
Silica ↑ → Viscosity ↑
Temperature ↑ → Viscosity ↓
Cooling Rate
Fast Cooling
Fast cooling → small crystals
Extrusive → volcanic
Slow Cooling
Slow cooling → large crystals
Intrusive → plutonic
Easy way to remember:
Fast = Small
Slow = Large
Porphyritic Texture
Porphyritic texture has:
Coarse crystals surrounded by fine crystals.
It forms through two cooling rates:
Slow → Fast
The magma:
Starts deep underground.Cools slowly, allowing large crystals to form.Erupts.The remaining magma cools quickly.Fine crystals form around the large crystals.
So:
Porphyritic = starts deep → slow cooling → erupts → fast cooling
FELSIC vs. MAFIC
FELSIC
High silica
Lots of quartz and feldsparLow Fe and MgAssociated with continental crust
Remember:
FELSIC = high silica + continental
MAFIC
Low silica
Ferromagnesian mineralsHigh Fe and MgAssociated with oceanic crust
Remember:
MAFIC = Fe/Mg + oceanic
Igneous Rock Bodies
Know these four:
Batholith
Large intrusive igneous body.
Example: Sierra Nevada Batholith
Stock
Intrusive igneous body smaller than a batholith.
Dike
Igneous body that cuts across existing rock.
Sill
Igneous body that forms parallel to existing rock.
Palisades
Palisades → Mafic sill
The review sheet connects the Palisades Sill with:
The breakup of Pangaea.
⭐ TEST MEMORY SHEET
If you want the absolute shortest version to memorize:
Physical Geology → internal + external processes
Historical Geology → sequence of events
Uniformitarianism → present is key to past
Scientific Method → Data → Hypothesis → Test → Theory
4 Spheres → Geo, Bio, Atmo, Hydro
EOS → satellites
3 Cycles → Hydrologic, Rock, Tectonic
Terrestrial → Mercury, Venus, Earth, Mars
Gas Giants → Jupiter, Saturn, Uranus, Neptune
Nebular Hypothesis → solar system
Accretion → planets form from accumulating material
Differentiation → Core, Mantle, Crust
Core → iron; inner solid, outer liquid
Mantle → Fe + Mg
Crust → Si + O
Earth unique → Biosphere
Atomic # → protons
Mass # → protons + neutrons
Isotopes → different neutrons
Ion → charged atom
Atomic substitution → similar size + charge
Olivine → Mg²⁺ ↔ Fe²⁺
Silicate → Si + O
Tetrahedron → (SiO₄)⁴⁻
Complex ion → >1 element
Rock → mixture of minerals
Pressure → melting point ↑
Water → melting point ↓
Geothermal gradient → temperature ↑ with depth
Fractional melting → some melts, some stays solid
Fractional crystallization → crystals separate from magma
High silica → thick/high viscosity
High temperature → thin/low viscosity
Fast cooling → small/extrusive/volcanic
Slow cooling → large/intrusive/plutonic
Porphyritic → slow → fast
Felsic → high silica, quartz/feldspar, continental
Mafic → low silica, Fe/Mg, oceanic
Batholith → Stock → Dike → Sill
Sierra Nevada → Batholith
Palisades → Mafic Sill → Pangaea breakup
CHAPTER 1 — INTRODUCTION
Physical Geology vs. Historical Geology
Physical Geology — focuses on Earth's internal and external processes.
Historical Geology — focuses on the sequence of events that happened throughout Earth's history.
"Rocks are Events" — rocks can record evidence of events that happened in Earth's past.
Scientific Inquiry
The goal of scientific inquiry is to find patterns and use them to make predictions.
Science assumes that the natural world is understandable.
A good scientific explanation should explain all available observations, while the simplest idea is usually the best.
What makes a good hypothesis?
A good hypothesis should:
Explain all available observations.Be simple.
Uniformitarianism
Uniformitarianism — the idea that the processes we observe today can help us understand Earth's past.
"THE PRESENT IS THE KEY TO THE PAST"
Scientific Method
Know the basic sequence:
Data → Hypothesis → Test → Theory
Data — observations and information collected by scientists.
Hypothesis — an initial idea or prediction that can be tested against observations.
Test — an experiment or other method used to test the hypothesis.
Theory — an idea that has been rigorously tested and supported over many years, leading to general agreement among scientists.
Glacial vs. Wind vs. Water-Laid Sediments
Know that glaciers, wind, and water can transport and deposit sediment.
The important distinction to recognize is the environment/process that deposited the sediment:
Glacial → deposited by glaciers/ice.Wind → deposited by wind.Water-laid → deposited by water.
Earth's 4 Spheres
Earth has four major interconnected spheres:
1. Geosphere
Geosphere → the solid Earth, including rocks and soil.
2. Biosphere
Biosphere → organic life.
3. Atmosphere
Atmosphere → the gases surrounding Earth.
4. Hydrosphere
Hydrosphere → all water and ice, including surface and underground water.
Two-way exchanges
The four spheres are interconnected, meaning materials and energy can move between them in two-way exchanges.
EOS — Earth Observing System
EOS — Earth Observing System
→ Satellites monitoring Earth's systems.
Three Interconnected Cycles
Know these three:
Hydrologic CycleRock CycleTectonic Cycle
They are interconnected cycles that operate within Earth's systems.
EARTH IN SPACE — THE SOLAR SYSTEM
4 Terrestrial vs. 4 Gas Giant Planets
Terrestrial planets
The four terrestrial planets are:
Mercury, Venus, Earth, Mars
They are the rocky planets.
Gas giant planets
The four gas giants are:
Jupiter, Saturn, Uranus, Neptune
Nebular Hypothesis
Nebular Hypothesis → explains the formation of the solar system.
Planetary Accretion
Planetary accretion → material comes together to form planets.
Chemical Differentiation
Chemical differentiation produced Earth's major layers:
Core → Mantle → Crust
Core
IronInner core = solidOuter core = liquid
Mantle
Iron- and magnesium-rich rocks
Crust
Silicon- and oxygen-rich rocks
The crust has two types:
Oceanic crustContinental crust
What Makes Earth Unique?
The review sheet specifically identifies the:
Biosphere
Earth has a biosphere that supports life.
CHAPTER 2 — MINERALS
Elements
An element is a basic type of matter made of atoms of the same element.
Atoms
Atoms contain:
Protons → positive charge
Neutrons → no charge
Electrons → negative charge
Atomic Number vs. Mass Number
Atomic number → number of protons.
Mass number → number of protons + neutrons.
Isotopes
Isotopes → atoms of the same element with different numbers of neutrons.
Atoms vs. Ions
Atom → electrically neutral when it has equal numbers of protons and electrons.
Ion → an atom that has gained or lost electrons and therefore has a charge.
Ionic vs. Covalent Bonds
Ionic bond → involves attraction between oppositely charged ions.
Covalent bond → atoms share electrons.
For minerals, remember that the silicon-oxygen bonds in the silicate structure are covalent and very strong.
Octet Rule
Octet rule → atoms tend to gain, lose, or share electrons to obtain a stable outer electron arrangement.
Atomic Substitution
Atomic substitution → one ion replaces another ion of similar size and charge.
Olivine
In olivine:
Mg²⁺ and Fe²⁺ can substitute for each other.
Why?
Because they have:
Similar sizeThe same charge
Olivine can therefore have:
Fe₂SiO₄
Mg₂SiO₄
or an intermediate mixture:
(Mg, Fe)₂SiO₄
Elemental Abundances in Continental Crust
Know the important elements listed on your review sheet:
Silicon (Si)
Oxygen (O)
The review sheet specifically wants you to know the abundance of Si and O in the continental crust.
Silicon-Oxygen Tetrahedron
The basic building block of silicate minerals is the:
Silicon-Oxygen Tetrahedron
Formula:
(SiO₄)⁴⁻
It contains:
1 Si4 O
So remember:
SiO₄ = 1 silicon + 4 oxygen
It is a complex ion because it contains more than one element.
Complex vs. Simple Ions
Simple ion → contains one element.
Complex ion → contains more than one element.
Example:
O²⁻ → simple ion
(SiO₄)⁴⁻ → complex ion
Mineral Types and Families
Know these mineral families from the review sheet:
Silicates
Contain silicon and oxygen.
SiO₄
They are the most abundant mineral group.
Carbonates
Contain the carbonate ion:
CO₃
Sulfides
Associated with sulfur (S).
Evaporites
The review sheet gives:
NaCl — halite
as the example to know.
CHAPTER 6 — IGNEOUS ROCKS
Melting Rocks
Rock is a mixture of minerals.
Because different minerals have different melting temperatures, rocks melt over a range of temperatures.
The review sheet gives approximately:
800–1,200°C
Geothermal Gradient
Geothermal gradient → the rate of temperature increase with depth.
The rate is approximately:
Ocean floor → 13°C/km
Continental crust → 6.7°C/km
The geothermal gradient is therefore about twice as rapid beneath the ocean floor as beneath continental crust.
Why Rocks in the Mantle Stay Solid
The temperature in the upper mantle can be above the melting point of rocks at Earth's surface.
However:
Pressure increases with depth → melting point increases
Therefore, the rocks can remain solid because of the increased pressure.
Pressure-Temperature Relationship
Remember:
Pressure ↑ → Melting point ↑
Water → Melting point ↓
These are two extremely important relationships for the test.
Fractional Melting vs. Fractional Crystallization
Fractional Melting
Rock contains many different minerals, and each mineral melts at a different temperature.
Therefore, only part of the rock may melt.
Fractional melt → only a fraction of the rock melts.
Fractionation → magma separates from the remaining solid material.
Basic idea:
Rock → partial melting → magma + solid
Fractional Crystallization
This is essentially the reverse of melting.
Crystals form and then separate from the magma.
Basic idea:
Magma → crystals separate → rock + remaining magma
The resulting rock and magma have different compositions from the original magma.
Three Factors Affecting Magmas and Lavas
Know these three:
CompositionTemperatureViscosity
Silica and Viscosity
High silica
High silica → high viscosity → thick
High temperature
High temperature → low viscosity → thin
Remember:
Silica ↑ → Viscosity ↑
Temperature ↑ → Viscosity ↓
Cooling Rate
Fast Cooling
Fast cooling → small crystals
Extrusive → volcanic
Slow Cooling
Slow cooling → large crystals
Intrusive → plutonic
Easy way to remember:
Fast = Small
Slow = Large
Porphyritic Texture
Porphyritic texture has:
Coarse crystals surrounded by fine crystals.
It forms through two cooling rates:
Slow → Fast
The magma:
Starts deep underground.Cools slowly, allowing large crystals to form.Erupts.The remaining magma cools quickly.Fine crystals form around the large crystals.
So:
Porphyritic = starts deep → slow cooling → erupts → fast cooling
FELSIC vs. MAFIC
FELSIC
High silica
Lots of quartz and feldsparLow Fe and MgAssociated with continental crust
Remember:
FELSIC = high silica + continental
MAFIC
Low silica
Ferromagnesian mineralsHigh Fe and MgAssociated with oceanic crust
Remember:
MAFIC = Fe/Mg + oceanic
Igneous Rock Bodies
Know these four:
Batholith
Large intrusive igneous body.
Example: Sierra Nevada Batholith
Stock
Intrusive igneous body smaller than a batholith.
Dike
Igneous body that cuts across existing rock.
Sill
Igneous body that forms parallel to existing rock.
Palisades
Palisades → Mafic sill
The review sheet connects the Palisades Sill with:
The breakup of Pangaea.
⭐ TEST MEMORY SHEET
If you want the absolute shortest version to memorize:
Physical Geology → internal + external processes
Historical Geology → sequence of events
Uniformitarianism → present is key to past
Scientific Method → Data → Hypothesis → Test → Theory
4 Spheres → Geo, Bio, Atmo, Hydro
EOS → satellites
3 Cycles → Hydrologic, Rock, Tectonic
Terrestrial → Mercury, Venus, Earth, Mars
Gas Giants → Jupiter, Saturn, Uranus, Neptune
Nebular Hypothesis → solar system
Accretion → planets form from accumulating material
Differentiation → Core, Mantle, Crust
Core → iron; inner solid, outer liquid
Mantle → Fe + Mg
Crust → Si + O
Earth unique → Biosphere
Atomic # → protons
Mass # → protons + neutrons
Isotopes → different neutrons
Ion → charged atom
Atomic substitution → similar size + charge
Olivine → Mg²⁺ ↔ Fe²⁺
Silicate → Si + O
Tetrahedron → (SiO₄)⁴⁻
Complex ion → >1 element
Rock → mixture of minerals
Pressure → melting point ↑
Water → melting point ↓
Geothermal gradient → temperature ↑ with depth
Fractional melting → some melts, some stays solid
Fractional crystallization → crystals separate from magma
High silica → thick/high viscosity
High temperature → thin/low viscosity
Fast cooling → small/extrusive/volcanic
Slow cooling → large/intrusive/plutonic
Porphyritic → slow → fast
Felsic → high silica, quartz/feldspar, continental
Mafic → low silica, Fe/Mg, oceanic
Batholith → Stock → Dike → Sill
Sierra Nevada → Batholith
Palisades → Mafic Sill → Pangaea breakup