Geology: Types of Rocks, Volcanoes, and Earthquake Mechanics

Forms when magma or lava cools and solidifies

Igneous Rock

Forms from the compaction or cementation of sediments

Sedimentary Rock

Forms when existing rock changes due to heat and pressure

Metamorphic Rock

Igneous rock that cools slowly below Earth's surface forming large crystals

Plutonic (Intrusive) Rock

Igneous rock that cools quickly at Earth's surface forming small crystals

Volcanic (Extrusive) Rock

Process by which minerals form as magma or lava cools

Crystallization

Process of turning loose sediments into solid rock through compaction and cementation

Lithification

Minerals precipitate from groundwater and bind sediment grains together

Cementation

Breaking down of rocks at Earth's surface by wind

water, or chemical reactions, Weathering

Transport of weathered material from one place to another

Erosion

Process where sediments settle after being transported

Deposition

Weight of overlying layers compresses deeper sediments

Compaction

Light-colored rocks high in silica such as granite and rhyolite

Felsic Rocks

Dark-colored rocks low in silica rich in iron and magnesium such as basalt and gabbro

Mafic Rocks

Rocks with intermediate silica content like andesite or diorite

Intermediate Rocks

Very low silica greenish rocks rich in olivine and pyroxene

Ultramafic Rocks

Plutonic mafic rock formed at mid-ocean ridges

Gabbro

Extrusive mafic rock forming most of oceanic crust

Basalt

Plutonic felsic rock rich in quartz and feldspar

Granite

Extrusive felsic rock equivalent to granite

Rhyolite

Volcanic intermediate rock found in volcanic arcs

Andesite

Intrusive intermediate rock equivalent to andesite

Diorite

Ultramafic intrusive rock from the Earth's mantle

Peridotite

Rare ultramafic extrusive rock with very low silica

Komatiite

Made from fragments of other rocks such as shale or sandstone

Clastic Sedimentary Rock

Forms when minerals precipitate from water such as rock salt or travertine

Chemical Sedimentary Rock

Formed from remains of organisms such as limestone or coal

Biochemical Sedimentary Rock

Fine-grained clastic rock forming in quiet water like river deltas

Shale

Medium-grained clastic rock forming at beaches or deserts

Sandstone

Chemical rock formed from evaporating saline water

Rock Salt

Biochemical rock formed from shells and marine organisms

Limestone

Biochemical rock formed in warm swampy environments

Coal

Chemical rock deposited by hot springs

Travertine

Broad gentle volcano made of low-viscosity basaltic lava flows

Shield Volcano

Steep layered volcano producing explosive eruptions

Composite Volcano

Rock fragments ejected from a volcano

Tephra

Fast-moving current of hot gas and volcanic matter

Pyroclastic Flow

Mudflow created when volcanic debris mixes with water

Lahar

Resistance of magma to flow depending on silica and temperature

Viscosity

Flows easily with low silica and high temperature

Low Viscosity Magma

Thick and explosive magma with high silica and low temperature

High Viscosity Magma

Temperature and chemical composition are the main factors affecting viscosity

Factors Affecting Viscosity

Stress builds before an earthquake then releases when it occurs

Stress Cycle

Underground point where earthquake begins

Hypocenter (Focus)

Point on the surface directly above the focus

Epicenter

Fault with vertical movement including normal and reverse faults

Dip-Slip Fault

Fault where hanging wall moves down from tension

Normal Fault

Fault where hanging wall moves up from compression

Reverse Fault

Fault involving horizontal movement

Strike-Slip Fault

Block of rock above the fault plane

Hanging Wall

Block of rock below the fault plane

Footwall

Horizontal line on an inclined rock surface indicating direction

Strike

Calculating P-S wave time difference from multiple stations

Epicenter Determination

Occurs when saturated soil loses strength and behaves like liquid

Liquefaction

Alignment of minerals in layers perpendicular to stress

Foliation

Alignment of long minerals in straight lines under stress

Lineation

Minerals grow larger during metamorphism

Recrystallization

Separation of light and dark minerals into bands

Gneissic Foliation

Low-grade metamorphic rock formed from shale

Slate

Medium-grade metamorphic rock with visible aligned minerals

Schist

High-grade metamorphic rock with banded texture

Gneiss

Metamorphic rock formed from sandstone

Quartzite

Metamorphic rock formed from limestone

Marble

Naturally occurring inorganic solid with crystalline structure and definite composition

Mineral

Orderly repeating arrangement of atoms in a solid

Crystalline Structure

Most abundant mineral group made of silicon and oxygen tetrahedra

Silicate Minerals

Mineral made of calcium carbonate (CaCO₃)

Calcite

Naturally occurring native element mineral

Gold

Common silicate mineral with formula SiO₂

Quartz

Rocks are made of one or more minerals

Rock vs Mineral

Molten rock that cools to form silicate minerals

Magma or Lava

Earth's crust is made mostly of oxygen

silicon, aluminum, iron, and calcium, Crust Composition

Mantle is rich in iron

magnesium, and sulfur, Mantle Composition

Example of a chemical element not a mineral

Potassium

Primary component that determines rock color and viscosity

Silica

Dark low-silica rocks rich in magnesium and iron

Mafic Rocks

Light high-silica rocks rich in quartz and feldspar

Felsic Rocks

Minerals align perpendicular to pressure forming flat planes

Foliation

Minerals form sheets or bands under directed stress

Gneissic Texture

Metamorphic change from shale to slate to schist to gneiss

Metamorphic Grade Sequence

Rock that cools below surface with large crystals

Intrusive Igneous Rock

Rock that cools quickly at the surface with small crystals

Extrusive Igneous Rock

Type of magma associated with shield volcanoes

Mafic Magma

Type of magma associated with composite volcanoes

Felsic Magma

Rocks that form by cooling at mid-ocean ridges

Gabbro and Basalt

Point on map representing earthquake origin above focus

Epicenter

Process where minerals form as magma solidifies

Crystallization

When rock melts and later cools to form new igneous rock

Igneous Rock Cycle Step

When rock is weathered eroded deposited

compacted and cemented, Sedimentary Rock Cycle Step

When rock is buried under heat and pressure to change form

Metamorphic Rock Cycle Step

Relationship between magma composition and eruption style

More silica = more explosive eruptions

Subduction zones produce high pressure and metamorphic rocks

Convergent Boundary Effects

Divergent boundaries produce mafic igneous rocks like basalt

Divergent Boundary Effects

Stress released along fractures in crust causing shaking

Earthquake

Earthquake hazard where wet soil behaves like fluid

Liquefaction

3D origin point of earthquake underground

Focus

Fault block that moves upward during reverse faulting

Hanging Wall

Fault block that moves downward during normal faulting

Footwall

Steep-sided volcano that erupts pyroclastic material

Composite Volcano

Broad dome-shaped volcano with gentle lava flows

Shield Volcano