Geology and Earth Resources

Earth

A dynamic planet that continually changes in structure.

Core

The dense, extremely hot metallic interior of Earth, mostly iron; solid at the center but fluid in the outer part, generating the magnetic field.

Mantle

The hot, pliable rocky layer surrounding the outer core; contains lighter elements such as oxygen, silicon, and magnesium.

Crust

The cool, brittle outer layer of rock; thin and dense under oceans, thick and light under continents.

Lithosphere

The rigid outer layer consisting of the crust and upper mantle; brittle and elastic in nature.

Asthenosphere

The weak, plastic zone beneath the lithosphere that allows tectonic plates to move.

Plate Tectonics

The theory describing large-scale movements and deformation of Earth’s lithospheric plates.

Continental Drift

Wegener’s hypothesis that continents once formed a single supercontinent (Pangaea) and later separated.

Pangaea

A prehistoric supercontinent meaning “all lands” that eventually split into the modern continents.

Seafloor Spreading

The creation of new oceanic crust at mid-ocean ridges as plates diverge.

Rift Zone

Region where the lithosphere is being stretched and split apart, often forming new ocean basins.

Triple Junction

Location where three tectonic plates meet, such as the Afar Depression in Ethiopia.

Subduction Zone

Region where one plate descends beneath another into the mantle, consuming oceanic crust.

Island Arc

A curved chain of volcanic islands formed at an ocean–ocean convergent boundary.

Mountain Building

Uplift and deformation of Earth’s crust due to collision and convergence of plates.

Transform Fault

Fracture where two lithospheric plates slide horizontally past each other (e.g., San Andreas Fault).

Divergent Boundary

Plate boundary where plates move apart and new crust forms from rising magma.

Convergent Boundary

Plate boundary where plates move toward one another, forming mountains or trenches.

Mineral

A naturally occurring, inorganic, solid substance with definite chemical composition and crystalline structure.

Silicates

The most abundant mineral group composed of silicon and oxygen, often with other elements.

Quartz

A hard, weathering-resistant silicate of silicon and oxygen; used in glassmaking and construction.

Feldspars

The most common minerals in the crust, composed of silicon, oxygen, aluminum, and alkali metals.

Ferromagnesian Minerals

Dark-colored silicates containing iron and/or magnesium, such as olivine.

Micas

Silicate minerals with sheet-like crystal structures that split easily into thin layers.

Clays

Sheet silicate minerals that can absorb or lose water; used in ceramics, construction, and drilling fluids.

Nonsilicates

Minerals grouped by common negative ions such as carbonates, sulfates, and halides.

Rock

A solid aggregate of one or more minerals or mineral materials bound together.

Igneous Rock

Rock formed by the cooling and solidification of molten magma.

Plutonic Rock

Coarse-grained igneous rock formed slowly beneath Earth’s surface (e.g., granite).

Volcanic Rock

Fine-grained igneous rock formed from lava cooling quickly at or near the surface (e.g., basalt, obsidian).

Obsidian

Natural volcanic glass produced by rapid cooling of lava without crystal formation.

Porphyry

Igneous rock containing large crystals (phenocrysts) in a fine-grained matrix.

Sediment

Unconsolidated material transported and deposited by wind, water, ice, or gravity.

Sedimentary Rock

Rock formed from compacted and cemented sediments near the Earth’s surface.

Clastic Sedimentary Rock

Rock composed of fragments of preexisting rocks, such as sandstone or shale.

Chemical Sedimentary Rock

Rock formed from precipitation of minerals out of solution, such as limestone.

Organic Sediment

Carbon-rich remains of living organisms that form materials such as coal.

Metamorphic Rock

Rock formed when preexisting rock is changed by heat, pressure, or chemical processes.

Contact Metamorphism

Alteration of rock caused by heat from nearby magma intrusions.

Regional Metamorphism

Widespread metamorphism resulting from high pressure and temperature during mountain building.

Foliation

Layered texture in metamorphic rocks resulting from alignment of platy minerals.

Slate

Fine-grained metamorphic rock derived from shale that splits easily into flat slabs.

Schist

Medium- to coarse-grained metamorphic rock rich in mica or similar minerals.

Gneiss

Banded metamorphic rock with alternating light and dark mineral layers.

Quartzite

Hard metamorphic rock formed from quartz-rich sandstone.

Marble

Metamorphic rock formed when limestone recrystallizes under heat and pressure.

Amphibolite

Metamorphic rock dominated by amphibole minerals; indicates moderate metamorphism.

Rock Cycle

The continuous process by which rocks of any type are transformed into other types through geological processes.

Economic Mineralogy

Study of minerals and rocks valuable for manufacturing and commerce.

Metals

Elements such as iron, aluminum, copper, and manganese essential for industrial use.

Nonmetals

Mineral resources such as sand, gravel, limestone, salts, and soils.

Placer Mining

Recovery of valuable minerals from stream sediments by washing and separation.

Underground Mining

Extraction of ores from beneath the surface through tunnels and shafts.

Open-pit Mining

Surface mining method that removes large volumes of overburden to expose ore.

Mountaintop Removal

Coal mining method that removes ridge tops, depositing waste in valleys.

Smelting

Heating ore to extract metals; often produces significant air pollution.

Heap-Leach Extraction

Process of dissolving metals from low-grade ore using chemical solutions like cyanide.

Conservation of Geological Resources

Effort to preserve mineral resources and minimize mining impacts.

Recycling

Reuse of metals and materials to conserve energy and reduce waste.

Minimills

Small-scale steel plants that recycle scrap metal efficiently and at lower energy cost.

New Materials

Alternatives such as polymers, ceramics, and fiber optics replacing traditional metals.

Earthquake

Sudden release of energy along faults causing ground movement.

Tsunami

Large sea wave generated by underwater earthquakes or landslides.

Volcano

Opening in Earth’s crust through which magma, gases, and ash erupt.

Landslide

Rapid downslope movement of soil or rock due to gravity.

Mass Wasting

Collective term for downslope movements of rock and soil under gravity.

Flood

Overflow of water onto normally dry land, often in river floodplains.

Beach Erosion

Natural redistribution of sand and sediments by wave motion.

Weather

Short-term local atmospheric conditions such as rain, snow, wind, or storms.

Climate

Long-term average of temperature, humidity, and precipitation patterns.

Greenhouse Effect

Warming of Earth caused by atmospheric gases trapping heat radiating from the surface.

Greenhouse Gases

Heat-trapping gases including water vapor, carbon dioxide, methane, nitrous oxide, and chlorofluorocarbons.

Global Warming

Long-term increase in Earth’s average surface temperature mainly due to fossil fuel combustion.

Climate Change

Long-term alteration of global or regional climate systems driven by human and natural factors.