Geology 1121K – Test 1 Study Guide (Modules 1–5)

Vocabulary flashcards covering the essential terms and definitions from Modules 1–5 for Geology 1121K Test 1. Use these cards to reinforce key concepts in physical and historical geology, plate tectonics, mineralogy, igneous processes, and volcanology.

Physical Geology

Branch of geology that examines Earth’s materials and the processes acting on them today.

Historical Geology

Branch of geology that studies Earth’s origin and its changes through geologic time.

Scientific Method

A systematic approach of observation, hypothesis formation, testing, and development of theories.

Hypothesis

A tentative, testable explanation for observed phenomena.

Theory

A well-substantiated explanation supported by a large body of evidence.

Rock Cycle

Concept describing the continuous transformation of igneous, sedimentary, and metamorphic rocks.

Principle of Uniformitarianism

Idea that present-day processes operated similarly in the geologic past (“the present is the key to the past”).

Alfred Wegener

German scientist who proposed the Continental Drift Hypothesis in 1915.

Continental Drift Hypothesis

Proposal that continents were once joined and have since moved apart.

Crust

Thin, outer chemical layer of Earth composed of low-density silicate rocks.

Mantle

Ultramafic, silicate layer between crust and core; makes up most of Earth’s volume.

Core

Central metallic layer of Earth, composed mainly of iron and nickel.

Lithosphere

Rigid physical layer consisting of crust and uppermost mantle; broken into tectonic plates.

Asthenosphere

Ductile, partially molten mantle layer beneath the lithosphere that allows plate motion.

Mesosphere (Lower Mantle)

Stronger, more rigid portion of the mantle below the asthenosphere.

Outer Core

Liquid iron-nickel layer that generates Earth’s magnetic field.

Inner Core

Solid iron-nickel sphere at Earth’s center.

Oceanic Crust

Thin, dense, basaltic portion of lithosphere beneath oceans.

Continental Crust

Thick, buoyant, granitic portion of lithosphere underlying continents.

Wilson Cycle

Model describing the opening, expansion, closing, and reassembly of ocean basins.

Divergent Plate Boundary

Tectonic setting where plates move apart under tensional forces.

Mid-Ocean Ridge (MOR)

Submarine mountain chain at divergent boundaries where new oceanic crust forms.

Rift

Linear continental valley formed as lithosphere stretches and thins at a divergent boundary.

Convergent Plate Boundary

Boundary where plates collide under compressional forces.

Subduction Zone

Region where one lithospheric plate descends beneath another into the mantle.

Collision Zone

Convergent boundary where two continents meet and buckle, forming high mountains.

Orogeny

Mountain-building event produced by tectonic forces at convergent margins.

Transform Plate Boundary

Boundary where plates slide past one another under shear stress.

Abyssal Plain

Extensive, flat deep-ocean floor away from mid-ocean ridges.

Oceanic Trench

Deep, narrow depression at a subduction zone.

Black Smoker (Hydrothermal Vent)

Hot, mineral-rich spring on the seafloor near a MOR emitting dark plumes.

Volcanic Arc

Curved chain of volcanoes above a subduction zone.

Island Arc

Volcanic arc on oceanic crust; erupts mainly mafic magma.

Continental Arc

Volcanic arc on continental crust; erupts mainly intermediate magma.

Accretionary Prism

Wedge of scraped-off sediments and rocks at a subduction margin.

Active Continental Margin

Edge of a continent that coincides with a plate boundary and active tectonism.

Passive Continental Margin

Tectonically quiet continental edge not at a plate boundary.

Triple Junction

Point where three plate boundaries meet.

Moho (Mohorovičić Discontinuity)

Seismic boundary between Earth’s crust and mantle.

Hot Spot

Stationary mantle plume that produces a chain of volcanoes as a plate moves over it.

Wadati-Benioff Zone

Dipping plane of earthquake foci outlining a subducting slab.

Age of Earth

Approximately 4.57 billion years.

Mineral

Naturally occurring, inorganic, crystalline solid with a definite chemical composition.

Silicate

Mineral group built from SiO₄ tetrahedra; most abundant in Earth’s crust and mantle.

Ferromagnesian Silicate

Dark, dense silicate containing iron and magnesium (e.g., olivine, pyroxene).

Nonferromagnesian Silicate

Light-colored silicate rich in Na, K, or Al (e.g., quartz, feldspar).

Chemical Bond

Force (ionic, covalent, metallic, etc.) that holds atoms together in a mineral.

Luster

Appearance of a mineral’s surface in reflected light (e.g., metallic, vitreous).

Hardness

Resistance of a mineral to scratching, measured by the Mohs scale.

Cleavage

Tendency of a mineral to break along planes of atomic weakness.

Euhedral Crystal

Mineral grain with well-developed, recognizable crystal faces.

Anhedral Crystal

Mineral grain lacking external crystal faces.

Polymorph

Minerals with the same composition but different structures (e.g., diamond vs. graphite).

Feldspar

Most common rock-forming silicate group; includes orthoclase and plagioclase.

Quartz

Hard, durable SiO₂ mineral; common in continental crust.

Olivine

High-temperature Mg-Fe silicate abundant in the mantle.

Rock

Coherent, naturally occurring aggregate of minerals or glass.

Magma

Molten rock beneath Earth’s surface.

Lava

Magma that erupts onto Earth’s surface.

Intrusive Igneous Rock

Rock that crystallized slowly below ground; coarse-grained (phaneritic).

Extrusive Igneous Rock

Rock that cooled quickly at the surface; fine-grained (aphanitic) or glassy.

Laccolith

Mushroom-shaped intrusion that domes overlying strata.

Sill

Tabular intrusion parallel to bedding planes.

Dike

Tabular intrusion that cuts across rock layers.

Pluton

Large, irregularly shaped intrusive igneous body.

Porphyritic Texture

Igneous texture with large crystals (phenocrysts) in a fine matrix.

Mafic Composition

Mg- and Fe-rich magma or rock; dark, low silica.

Intermediate Composition

Magma or rock with silica content between mafic and felsic; typically andesitic.

Felsic Composition

Silica-rich magma or rock; light-colored (granite, rhyolite).

Ultramafic Composition

Very Mg-Fe-rich, low-silica composition (peridotite, komatiite).

Viscosity

Resistance of magma or lava to flow; rises with silica content and falls with temperature and volatiles.

Bowen’s Reaction Series

Sequence in which minerals crystallize from cooling magma.

Partial Melting

Process where some minerals melt while others remain solid, producing magma.

Fractional Crystallization

Removal of early-formed crystals, changing magma composition.

Assimilation

Incorporation of surrounding rock into magma; xenoliths are evidence.

Magma Mixing

Blending of two magmas to form hybrid compositions.

Pillow Basalt

Bulbous basaltic lava formed by underwater extrusion.

Volcano

Vent and associated landform through which magma, gases, and pyroclasts erupt.

Effusive Eruption

Quiet eruption dominated by low-viscosity lava flows.

Explosive Eruption

Violent eruption driven by high viscosity and gas pressure.

Shield Volcano

Broad, gently sloping volcano built of fluid basaltic lavas.

Composite (Stratovolcano)

Steep, conical volcano of alternating lava flows and pyroclastic layers; andesitic magma.

Cinder Cone

Small, steep volcano made mostly of loose pyroclastic fragments.

Flood Basalt

Extensive plateau of stacked basalt flows erupted from fissures.

Pahoehoe

Smooth, ropy basaltic lava flow texture.

Aa

Rough, blocky basaltic lava flow texture.

Pyroclastic Material (Tephra)

Fragmented volcanic debris ejected during an eruption.

Volcanic Ash

Fine pyroclastic particles smaller than 2 mm in diameter.

Volcanic Bomb

Molten pyroclastic fragment larger than 64 mm that solidifies in flight.

Lahar

Fast-moving volcanic mudflow of water and debris.

Crater

Small, circular depression at a volcano’s summit surrounding the vent.

Caldera

Large depression formed by collapse after emptying of a magma chamber.

Magma Chamber

Subsurface reservoir that supplies magma to a volcano.

Parasitic Cone

Small cone on the flank of a larger volcano fed by a secondary vent.

Lava Dome

Steep-sided mound of viscous felsic lava piling up near a vent.

Columnar Basalt

Hexagonal columns formed as thick basaltic lava cools and contracts.

Plate Motion Rate

Tectonic plates move roughly 1–15 cm per year.

Ridge-Push & Slab-Pull

Main mechanisms driving plate movement along with mantle convection.