Geology Practice Flashcards

A set of question-and-answer flashcards based on lecture notes covering minerals, igneous rocks and processes, sedimentary rocks, weathering, erosion, and metamorphic rocks.

What is the Mohs hardness scale?

A scale from $1\text{--}10$ that measures how hard a mineral is.

How do you measure mineral hardness?

By scratching one mineral with another.

What is required for something to be a mineral?

It must be naturally occurring, inorganic, solid, have a crystal structure, and have a definite chemical composition.

What is cleavage?

The way a mineral breaks along flat, weak planes.

Which mineral group is most common on Earth?

Silicates.

What is a lahar?

A mudflow made of volcanic material and water.

What is a pyroclastic flow?

A fast, extremely hot flow of gas, ash, and rock.

What is ash distribution?

Volcanic ash being carried and spread by wind over large areas.

What is the difference between intrusive and extrusive igneous rocks?

Intrusive rocks form underground and cool slowly; extrusive rocks form at or near the surface and cool quickly.

Where do intrusive igneous rocks form?

Underground.

Where do extrusive igneous rocks form?

At or near Earth's surface.

How does temperature affect magma viscosity?

Hotter magma has lower viscosity; cooler magma has higher viscosity.

What is a glassy texture?

A texture with no visible crystals because the rock cooled extremely quickly.

How do igneous rocks form?

By the cooling and solidification of magma or lava.

What is decompression melting?

Rock melts when pressure decreases, usually at divergent boundaries or hotspots.

What is flux melting?

Water lowers the melting point of rock, commonly at subduction zones.

What is heat transfer melting?

Hot magma heats nearby rock until it melts.

How does a stratovolcano form and look?

Layers of lava and ash build a steep, cone-shaped volcano.

How does a shield volcano form and look?

Runny lava builds a wide volcano with gentle slopes.

How do clastic sedimentary rocks form?

From pieces or fragments of other rocks.

How do organic sedimentary rocks form?

From accumulated plant or animal remains.

How do chemical sedimentary rocks form?

When minerals precipitate out of water.

How do biochemical/bioclastic sedimentary rocks form?

From accumulated shells, skeletons, or other mineral material produced by organisms.

Where do sedimentary rocks generally form?

At or near Earth's surface, especially in water environments.

Which type of sedimentary rock forms from pieces of other rocks?

Clastic.

Which type of sedimentary rock forms from precipitation of minerals in seawater?

Chemical.

What is the typical texture of clastic sedimentary rocks?

Visible grains, pieces, or fragments of other rocks.

How is grain size related to environmental energy?

Large grains indicate high-energy environments; small grains indicate low-energy environments.

What type of sedimentary rock is salt?

Chemical sedimentary rock.

What is weathering?

The breaking down of rocks at Earth's surface.

What is erosion?

The movement of sediment by wind, water, ice, or gravity.

What is deposition?

The dropping or settling of sediment.

What is chemical weathering?

Weathering that chemically changes or dissolves rock.

What is physical weathering?

The breaking of rock into smaller pieces without changing its chemical composition.

What are common types of physical weathering?

Frost wedging, root wedging, and abrasion.

What are common types of chemical weathering?

Oxidation, dissolution, and hydrolysis.

What is frost wedging?

Water enters cracks, freezes and expands, causing the rock to break.

What is root wedging?

Plant roots grow into cracks and force rocks apart.

What is contact metamorphism?

Heat from nearby magma changes surrounding rock.

Where does contact metamorphism occur?

Around magma intrusions.

What is regional metamorphism?

Heat and pressure change large areas of rock, usually near convergent plate boundaries.

How hot do rocks need to be for metamorphism?

Usually above about $150^\circ\text{C}$ but below their melting point.

What is the most common metamorphic texture?

Foliated texture.