GEOL107 Exam 1 chap 1-4

CHAPTER 1

Why geology matters

Geology matters because it helps humans find resources, avoid hazards, and protect the environment

Define crust, mantle, core

crust - thin rocky outer layer; mantle - thick layer of hot solid rock that flows slowly; core - metallic center (iron and nickel)

Lithosphere vs. asthenosphere

lithosphere - rigid crust and upper mantle (tectonic plates); asthenosphere - softer, "plastic" mantle layer plates move on

Divergent boundary

plates pull apart and new crust forms (i.e. Mid-Atlantic Ridge)

Convergent boundary

plates collide and it leads to subduction/mountains (i.e. Andes Mountains)

Transform boundary

plates slide past each other and it leads to earthquakes (i.e. San Andreas Fault)

Subduction

one plate sinks under another at a convergent boundary

Rift valley

long depression where crust is pulling apart

Isostatic adjustment

crust rises/ sinks to "float" evenly on the mantle

Theory (scientific)

a well-tested explanation supported by evidence (not a guess)

CHAPTER 2

What five criteria define a mineral, and why are glass or coal excluded?

A mineral must be: naturally occurring, inorganic, a solid, have an orderly crystal structure, and a definite chemical composition. Glass is excluded because it has no crystal structure, and coal is excluded because it is organic

Which physical properties are most reliable for identifying minerals?

The most reliable properties are hardness, streak, luster, cleavage/fracture, and crystal form (plus density/specific gravity).Color is less reliable because impurities can change it

How does atomic structure influence mineral properties such as hardness and cleavage?

Atomic structure controls how tightly atoms bond. Strong bonds = harder minerals, and weak bonds in certain planes = cleavage (minerals break smoothly along those weak layers)

What is the silicon-oxygen tetrahedron and why is it important?

It's the basic building block of most silicate minerals: 1 silicon atom bonded to 4 oxygen atoms in a tetrahedron shape.It's important because silicates make up most of Earth's crust

How do silicate tetrahedra link together to form different mineral groups?

Tetrahedra connect by sharing oxygen atoms to form: isolated tetrahedra, chains (single/double), sheets, frameworks (More sharing = stronger structures and different properties)

Examples of framework, chain, and sheet silicate minerals

Framework: quartz, feldspar

Chain: pyroxene (single chain), amphibole (double chain)

Sheet: mica (biotite/muscovite), clay minerals

Major non-silicate mineral groups and why they're important

Key groups:

carbonates (calcite)

oxides (hematite)

sulfides (pyrite, galena)

sulfates (gypsum)

halides (halite)

native elements (gold, copper) They're important because they are major ores, building materials, and key to environmental chemistry

How do minerals control soil chemistry and resource availability?

As minerals weather, they release nutrients (like K, Ca, Mg, Fe) and affect soil pH.Clay minerals also help soils hold water and nutrients, which controls plant growth and fertility

Why is studying minerals important to geology and environmental science?

Minerals reveal how rocks form, help locate resources (metals, groundwater), and explain hazards like acid mine drainage and contamination. They also control soil and water chemistry, which directly affects ecosystems and human health

What is the Mohs Hardness Scale and how is it used?

The Mohs scale ranks minerals from 1 (talc) to 10 (diamond) based on scratch resistance. You use it by seeing which material scratches another to estimate hardness

CHAPTER 3

Differences between magma and lava + how they influence rock formation

Magma is molten rock below Earth's surface; lava is molten rock at the surface. Magma cools slowly underground → coarse crystals; lava cools quickly at surface → fine crystals or glass

How does cooling rate affect igneous texture?

Slow cooling → large crystals (phaneritic)

Fast cooling → tiny crystals (aphanitic)

Instant cooling → glassy texture

Two-stage cooling → porphyritic (big crystals in fine groundmass)

Intrusive vs extrusive igneous rocks

Intrusive (plutonic): forms underground, slow cooling, coarse-grained (ex: granite, gabbro)

Extrusive (volcanic): forms at surface, fast cooling, fine-grained/glassy/vesicular (ex: basalt, rhyolite, pumice)

Bowen's Reaction Series + crystallization order

Bowen's series shows minerals crystallize in a predictable order as magma cools:high-temp minerals (mafic) form first → low-temp minerals (felsic) form last. It explains why different magmas create different rock types

Why do certain minerals commonly occur together?

Because minerals form under the same temperature + chemical conditions, so minerals that crystallize at similar temps tend to appear together (ex: olivine + pyroxene; quartz + K-feldspar)

Textures from gases trapped in lava + what they reveal

Trapped gas bubbles make vesicular texture.It shows lava contained volatile gases and cooled quickly, often in explosive or gas-rich eruptions (ex: scoria, pumice)

How composition affects color and density

Mafic minerals (Fe/Mg-rich) → dark color, high density

Felsic minerals (silica-rich) → light color, lower density This is why basalt is darker/denser than granite

Why igneous rocks matter scientifically + economically

Scientifically: record Earth's interior processes, plate tectonics, and magma history

Economically: source of valuable ores (Cu, Ni, Fe), building stone (granite), and geothermal energy areas

CHAPTER 4

What factors control the style of volcanic eruptions?

Eruption style is mainly controlled by magma viscosity and gas content

Low viscosity + low trapped gas → effusive (lava flows)

High viscosity + lots of trapped gas → explosive (ash + pyroclastics)

How does magma composition influence viscosity and eruption behavior?

Higher silica = higher viscosity because silica forms "sticky" networks

Basaltic (low silica): runny → gases escape → gentler eruptions

Rhyolitic (high silica): sticky → gases trapped → violent eruptions

Differences between shield volcanoes, stratovolcanoes, and cinder cones

Shield volcano: broad, gentle slopes; basaltic lava; mostly effusive (ex: Hawaii)

Stratovolcano (composite): tall, steep; layers of lava + ash; often explosive (ex: Mt. St. Helens)

Cinder cone: small, steep; loose pyroclastic fragments; short-lived eruptions (ex: Parícutin)

Basaltic vs rhyolitic eruptions + hazards

Basaltic magma: effusive eruptions → lava flows, lava fountains, volcanic gases

Rhyolitic magma: explosive eruptions → ash fall, pyroclastic flows, caldera formation

Rhyolitic hazards are usually more widespread + deadly

Volcano distribution & plate tectonics

Most volcanoes form at plate boundaries:

Divergent boundaries: mid-ocean ridges (basaltic volcanism)

Convergent boundaries: subduction zones (stratovolcanoes)

Hotspots: within plates (ex: Hawaii, Yellowstone)

Pyroclastic flows vs lahars + why they're dangerous

Pyroclastic flow: fast-moving hot gas + ash + rock; extremely deadly, can't be outrun

Lahar: volcanic mudflow (ash + water + debris); follows valleys and can bury towns. Both move quickly and cause massive destruction with little warning

How volcanic eruptions impact global climate

Big eruptions inject SO₂ and ash into the stratosphere, creating sulfate aerosols that reflect sunlight, causing short-term global cooling (months to a few years)

Examples of major historic eruptions + consequences

Mount St. Helens (1980): pyroclastic flows, landslides, major destruction

Krakatoa (1883): huge explosion, tsunamis, global cooling

Tambora (1815): strongest in modern history; caused the "Year Without a Summer"

Pinatubo (1991): major global cooling due to aerosol release

Benefits volcanoes provide to humans

Volcanoes create:

fertile soils for farming

geothermal energy

valuable minerals (gold, copper, sulfur)

new land + tourism (islands, scenic parks)