1-2: Rock Cycle and Introduction

Geology

The study of the Earth—its structure, materials, processes, and history.

Engineering Geology

The application of geological principles and information to the design, construction, and maintenance of engineering works and the remediation of environmental problems.

Uniformitarianism

The principle that geological processes operating today have operated similarly throughout Earth's history ("The present is the key to the past").

Catastrophism

The theory that Earth's features are largely shaped by sudden, short-lived, violent events.

James Hutton

Scottish geologist, founder of modern geology, proposed uniformitarianism and the concept of deep geological time.

Charles Lyell

Scottish geologist who championed and spread the principle of uniformitarianism.

Georges Cuvier

French naturalist, founder of paleontology, advocated for catastrophism and established extinction as fact.

Earth's Age

Approximately 4.57 billion years old.

Chemical Layers of Earth

Crust, Mantle, Core (classified by composition).

Mechanical Layers of Earth

Lithosphere, Asthenosphere, Mesosphere, Outer Core, Inner Core (classified by physical state/behavior).

Crust

Earth's outermost chemical layer; continental crust is granitic, oceanic crust is basaltic; mostly igneous and metamorphic rock.

Lithosphere

Rigid mechanical layer comprising the crust and the uppermost solid mantle; broken into tectonic plates.

Asthenosphere

Ductile, partially molten layer of the mantle below the lithosphere where convection occurs.

Mantle

Thick chemical layer composed primarily of iron and magnesium silicate minerals.

Mesosphere

The lower, strong, solid part of the mantle beneath the asthenosphere.

Outer Core

Liquid mechanical layer, composed mainly of iron, generates Earth's magnetic field.

Inner Core

Solid mechanical layer, composed mainly of iron, solid due to immense pressure.

Geothermal Gradient

The rate of temperature increase with depth within Earth; roughly 30°C per km in the crust.

Convection Cells

Circular movement of material in the mantle driven by heat from the core, driving plate tectonics.

Mineral

A naturally occurring, inorganic, crystalline solid with a definite chemical composition and specific crystal structure.

Rock

A naturally occurring solid aggregate of one or more minerals or mineraloids.

Crystal Lattice

The specific, repeating three-dimensional arrangement of atoms in a mineral.

Igneous Rock

Rock formed from the cooling and solidification of magma or lava.

Sedimentary Rock

Rock formed from the compaction and cementation of sediments, or precipitation from solution.

Metamorphic Rock

Rock formed when existing rock is subjected to high heat, pressure, and/or chemical fluids.

The Rock Cycle

A conceptual model describing the continuous transitions of rock material between igneous, sedimentary, and metamorphic states.

Magma

Molten rock beneath Earth's surface.

Lava

Magma that erupts onto Earth's surface.

Extrusive Igneous Rock

Fine-grained igneous rock formed from lava cooling rapidly at Earth's surface.

Intrusive Igneous Rock

Coarse-grained igneous rock formed from magma cooling slowly beneath Earth's surface.

Weathering

The breakdown of rocks at Earth's surface by physical, chemical, or biological processes.

Erosion

The transportation of weathered material by wind, water, or ice.

Sediment

Weathered and eroded rock fragments or chemical precipitates.

Lithification

The process converting sediment into solid rock via compaction and cementation.

Metamorphism

The process that changes a rock's mineralogy, texture, or chemical composition due to heat, pressure, and/or hydrothermal fluids.

Uplift

The geological process that brings deeply buried rocks to the surface.

Parent Rock

The original rock from which a new rock (e.g., metamorphic or soil) is derived.

Mineral Properties

Characteristics used for identification: color, streak, luster, cleavage, fracture, hardness, specific gravity, crystal form.

Cleavage

A mineral's tendency to break along planes of weak atomic bonding, producing smooth, flat surfaces.

Fracture

The way a mineral breaks when it does not exhibit cleavage (e.g., conchoidal, uneven).

Mohs Hardness Scale

A relative scale from 1 (talc) to 10 (diamond) ranking a mineral's resistance to scratching.

Specific Gravity

The ratio of a mineral's density to the density of water; a measure of its relative heaviness.

Silicate Minerals

The largest and most abundant mineral group, based on the silica tetrahedron (SiO₄)⁴⁻ building block.

Rock-Forming Minerals

The relatively few minerals (e.g., quartz, feldspars, micas, amphiboles, pyroxenes, olivine) that make up most rocks.

Soil

Unconsolidated material at Earth's surface formed by weathering of rock, composed of mineral particles, organic matter, water, and air.

Clay Minerals

Fine-grained, sheet silicate minerals (e.g., kaolinite, montmorillonite) in soils; often exhibit shrink-swell behavior.

Natural Materials (Engineering Context)

Geological materials like soils and rocks; they are variable and non-homogeneous, unlike manufactured building materials.

Site Investigation

Critical engineering geology task to evaluate distribution and properties of natural materials before design and construction.

Saint Francis Dam Collapse (1928)

A catastrophic engineering failure in the USA that highlighted the need for geological input in dam design.