GEOL101

Geology

Geology

The study of Earth processes

Catastrophism

The theory that the Earth was shaped through natural disasters

uniformitarianism

Physical, chemical, and biological laws that operate today also operated in the geologic past

Minerals

The fundamental unit that makes up rocks

Igneous rocks

Rocks formed from cooled magma

Sedimentary rocks

Rocks formed from weathering processes

Metamorphic rocks

Rocks formed from metamorphism caused by heat and pressure

Ionic bond

one atom donates valence electrons and another atom accepts them

Atom

The smallest particle of matter that cannot be chemically split (though it can be split via nuclear fission); composed of protons, electrons, and neutrons.

Element

A substance defined by the number of protons in its nucleus; particles sharing this number have identical chemical and physical properties.

Periodic Table

An organized depiction of all known chemical elements, developed by Dmitri Mendeleev in 1869.

Valence Electrons

Electrons occupying an atom's outermost shell; involved in forming chemical bonds.

Chemical Bond

Formed when atoms share their outer electrons with each other.

Octet Rule

The principle that atoms gain, lose, or share electrons until reaching a stable count of 8 outer electrons.

Ionic Bond

Occurs when one atom donates outer electrons and another atom accepts them; example: sodium chloride (NaCl).

Covalent Bond

Occurs when two atoms share a pair of electrons; example: water (H2O).

Metallic Bond

Occurs when atoms contribute electrons to a shared, freely moving pool; example: copper's high electrical conductivity.

Mineral (definition)

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

Rock

A naturally occurring solid composed of minerals or other natural planetary materials; example: coal.

Mineral Chemical Formulas

Can range from a single element (native sulphur, S) to combinations of elements (halite, NaCl; potassium feldspar, KAlSi3O8); physical characteristics depend on composition and atomic arrangement.

Mineral Formation Processes

Includes crystallization of molten magma, weathering or chemical precipitation, and metamorphism (heat and pressure transforming one type into another).

Laboratory Mineral Identification Methods

Techniques such as optical microscopes, optical spectroscopy, X-ray fluorescence, and X-ray scattering used to study composition and structure.

Field/Lab Mineral Identification

Relies on easily observable physical characteristics that can be tested in an undergraduate lab or out in the field.

Key Mineral Properties

A set of physical and chemical characteristics — including luster, color, streak, crystal shape, resistance to breaking, hardness, density, breakage style, magnetism, acid reaction, feel, and taste — used to tell specimens apart.

Luster

The description of how a mineral reflects light; split into metallic (reflects like a coin) and nonmetallic (glassy, dull, earthy, or pearly) types.

Color (as a mineral property)

Often unreliable for identification since many hues come from impurities trapped in the crystal lattice, though some minerals show consistent or diagnostic hues.

Streak

The color of the powder produced when a mineral is dragged across a ceramic plate.

Double Refraction

A rare optical effect, seen mainly in calcite, where the crystal structure splits light into two images.

Crystal Habit

The shape that a crystal ideally takes, such as cubic, sheet-like, eight-sided, bladed, tabular, or massive (no distinct shape).

Euhedral Crystal

A crystal that formed in optimal conditions with clearly defined faces; from the Greek for good face.

Anhedral Crystal

A crystal that formed in a competitive environment, leaving no space for distinct faces to develop.

Tenacity

A measure of resistance to breaking, bending, or cutting; types include brittle, malleable, sectile, and elastic behavior.

Hardness / Mohs Scale

Resistance to scratching, measured on a scale from 1 (softest, talc) to 10 (hardest, diamond).

Cleavage

The tendency to break along smooth, repeating planes of weaker chemical bonds, determined by crystal structure.

Fracture

Irregular breakage that occurs in minerals lacking planes of weakness; types include irregular, splintery, fibrous, and conchoidal (rippled, like a mussel shell).

Density and Specific Gravity

Mass per unit volume, or (more commonly used by mineralogists) the ratio of a substance's weight to the weight of an equal volume of water.

Effervescence

The bubbling reaction some carbonate minerals, such as calcite, show when exposed to dilute hydrochloric acid.

Magnetism (mineral property)

A property of iron-bearing minerals like magnetite that causes them to attract objects such as paperclips.

Feel (mineral property)

How a mineral's surface responds to touch — for example, soapy or slippery (talc) versus greasy (graphite).

Taste and Radioactivity (mineral properties)

Some minerals, like halite, have a distinctive flavor when licked, while others emit particles that can trigger a Geiger counter.

Rock-Forming Minerals

A small subset of the roughly 6,000 known minerals that are abundant enough to make up most rocks; only 8 elements account for over 98% of Earth's crust.

Silicates vs. Nonsilicates

The two broad mineral categories, distinguished by whether or not they contain the SiO4 base structure in their chemical formula.

Silicon-Oxygen Tetrahedron

A complex ion with a -4 charge, made of one silicon atom bonded to four oxygen atoms; serves as the fundamental building block of silicate minerals.

Silicate Structures

The different arrangements — independent units, single chains, double chains, sheets, or 3D frameworks — that silicate building blocks can form, which define separate mineral groups.

Olivine Group

A group of high-temperature, ferromagnesian silicates with isolated tetrahedra; black to olive-green with glassy luster and conchoidal fracture; makes up most of Earth's upper mantle.

Pyroxene Group

A diverse group of ferromagnesian silicates with tetrahedra arranged into single chains; a key component of basalt and other dark igneous rocks (e.g., augite, diopside).

Amphibole Group

A ferromagnesian silicate group with tetrahedra arranged into double chains and unique cleavage at 60° and 120°; often forms elongate, bladed crystals; includes the minerals that make up asbestos.

Mica Group

A silicate group with tetrahedra arranged into sheets, giving these minerals a flexible, layered structure; common types include muscovite and biotite.

Feldspar Group

The most plentiful silicate group in Earth's crust; a nonferromagnesian silicate with tetrahedra arranged into a three-dimensional network, divided into a potassium-rich type (often salmon-pink) and a calcium/sodium-rich type (often white-grey to black).

Quartz

The only common silicate made entirely of silicon and oxygen (SiO2), with a fully shared 3D tetrahedral structure; relatively hard and extremely resistant to weathering.

Clay Minerals

A group of fine-grained minerals that form from the weathering of other silicates, with tetrahedra arranged into sheets; an important part of sedimentary environments.

Carbonates (nonsilicates)

The most common nonsilicate mineral group, defined by a polyatomic ion containing carbon and oxygen; the most common example is calcite (CaCO3).

Sulphates (nonsilicates)

A nonsilicate mineral group containing a polyatomic ion made of sulfur and oxygen; the most common example is gypsum (CaSO4·2H2O).

Sulphides (nonsilicates)

A nonsilicate mineral group in which a metal is bonded directly to sulfur; important as metal ores (e.g., galena, pyrite).

Halides (nonsilicates)

A nonsilicate mineral group in which elements are bonded to a halogen such as fluorine or chlorine; the most important example is halite (NaCl).

Oxides (nonsilicates)

A nonsilicate mineral group in which a metal is bonded to oxygen; examples include hematite, magnetite, and ice.

Native Elements (nonsilicates)

Minerals that occur as pure, uncombined chemical elements in crystalline form, such as copper, sulphur, and graphite.

Phosphates (nonsilicates)

A nonsilicate mineral group containing a polyatomic ion made of phosphorus and oxygen; forms bones and tooth enamel as apatite.

Economically Important Minerals

Minerals valued for practical or commercial uses, such as gypsum for drywall, halite for table salt, hematite for iron ore, and micas for cosmetics; extracting them can also cause environmental impacts.

Magma Viscosity

Measure of molten rock’s resistance to flow, depends on composition and temperature

Types of eruptions

Effusive and Explosive

Effusive Eruptions

Characteristic of basaltic volcanoes, triggered by influx of new magma to volcanic system

Weathering

Breakdown of rocks, done physically and chemically

Erosion

Movement of weathered product to another location by erosional agents

Mechanical weathering

Physical forces that break rock into smaller pieces without changing the rock’s mineral composition

Chemical weathering

Chemical transformation of a rock into one or new compounds

Mechanisms of Mechanical Weathering

• Frost wedging

• Salt crystal growth

• Thermal stressing

• Sheeting

• Biological activity

Frost wedging

When rocks break apart because water freezes inside their cracks

Salt Crystal Growth

Evaporated water leaves behind salt crystals, occurs on rocky shorelines and arid regions

Thermal stressing

Occurs with cycles of heating and cooling; As heating occurs, rock expands and as cooling occurs, rock contracts.

Sheeting

When rock slabs separate due to them being exposed to erosion

Oxidation

Oxygen reacts with rocks and minerals, resulting in the decomposition of ferromagnesian silicates into the minerals hematite and limonite

Dissolution

Chemical breakup of a mineral by a solvent to produce a solution

Hydrolysis

Water reacts with a mineral and produces a different mineral, important process for decomposing silicates (Commonly how clay minerals form)

Hydration

Water is added to a mineral (Ex: Anhydrite to Gypsum)

Spheroidal Weathering

When chemical weathering creates rounded shapes from angular rock

Lithification

Process that turns unconsolidated sediments into solid sedimentary rocks

Metamorphism (geology)

When a rock has changes to its:

• Texture

• Internal Structure

• Composition

Physical geology

The study of understanding active Earth processes

Earth’s spheres

• Atmosphere

• Hydrosphere

• Biosphere

• Geosphere

Atmosphere

Gaseous outer layer of Earth

Hydrosphere

Water on the Earth

Biosphere

Earth’s life

Geosphere

Solid Earth, has 3 distinct layers

Crust

Outer layer of Earth, part of Geosphere

Mantle

Middle layer of earth, part of Geosphere

Core

Split into liquid outer core and solid inner core

Solar nebula theory

The Earth was formed 4.6 billion years ago from gas and dust

Ultramafic Rocks

Very low in silica, highly enriched in Mg/Fe, Igneous

Mafic Rocks

Low in silica, high in dark silicates, Igneous

Intermediate Rocks

In between Mafic and Felsic

Felsic Rocks

Highly enriched in silica/light silicates, low in Mg/Fe

Tephra

Fragmented magma

Shield volcanoes

Volcanoes with broad, domed shapes

Stratovolcanoes

Volcanoes with tall, steep sides formed from alternating lava flows and pyroclastic material

Index minerals

Minerals present in metamorphic rock, informs geologists of the conditions of metamorphism