Igneous Rocks and Intrusive Activity

Questions and Answers

What is an igneous rock?

Rocks formed from sediment deposition.

Rocks that are formed under extreme pressure.

Rocks that result from the erosion of other rocks.

Rocks formed by the cooling and solidifying of molten materials. (correct)

What is an intrusive rock?

Igneous rock formed from magma forced into older rocks at depths within the Earth's crust.

What is an intrusive body?

Produced when magma is forcibly injected into a fracture or zone of weakness.

What is a batholith?

A large mass of intrusive igneous rock larger than 100 square kilometers. Signup and view all the answers

What defines a laccolith?

A sheet intrusion that has been injected between two layers of sedimentary rock. Signup and view all the answers

What is the function of a dike in geology?

Any geologic body which cuts across flat wall rock structures. Signup and view all the answers

What is a sill?

A tabular sheet intrusion that has intruded between older layers of sedimentary rock. Signup and view all the answers

What is andesite?

An extrusive rock intermediate in composition between rhyolite and basalt. Signup and view all the answers

What characterizes pumice?

A light-colored, extremely porous igneous rock formed during explosive volcanic eruptions. Signup and view all the answers

What is obsidian?

A naturally occurring volcanic glass formed as an extrusive igneous rock. Signup and view all the answers

What defines granite?

A light-colored igneous rock with visible grains formed from the slow crystallization of magma. Signup and view all the answers

What is country rock?

Rock native to an area. Signup and view all the answers

What happens during contact metamorphism?

The mineralogy and texture of a body of rock are changed by exposure to pressure and extreme temperature from intruding magma. Signup and view all the answers

What is an extrusive rock?

Igneous volcanic rock formed from magma that flows out onto the surface as lava. Signup and view all the answers

What are felsic rocks?

Igneous rocks that are relatively rich in elements that form feldspar and quartz. Signup and view all the answers

What does mafic refer to?

Describes silicate minerals or igneous rocks that are rich in magnesium and iron. Signup and view all the answers

What is feldspar?

A very common igneous rock that makes up more than half of the Earth's crust. Signup and view all the answers

Study Notes

Igneous Rocks

Formed by cooling and solidifying of molten materials.
Can be classified as intrusive or extrusive based on their formation location.

Intrusive Rocks

Also known as plutonic rocks.
Formed from magma that cools slowly within the Earth's crust, leading to larger crystal sizes.
Common types include granite and diorite.

Extrusive Rocks

Form when magma erupts onto the Earth's surface as lava or ash.
Typically cool quickly, resulting in small or no visible crystals.
Examples include basalt, rhyolite, pumice, and obsidian.

Intrusive Bodies

Created by magma injected into fractures or zones of weakness.
Can lead to various geological formations.

Batholiths

Large mass of intrusive rock covering over 100 square kilometers.
Typically composed of granite or similar rocks.

Laccoliths

Sheet-like intrusive bodies injected between sedimentary rock layers.
The overlying rock is pushed upward, creating a dome shape.

Dikes

Geologic bodies that cut across existing rock layers and structures.
Often form in vertical or near-vertical orientations.

Sills

Tabular sheet intrusions that lie parallel to pre-existing rock layers.
Injected between older sedimentary rock or along foliations in metamorphic rock.

Andesite

Intermediate extrusive rock between rhyolite and basalt.
Characterized by moderate viscosity, forming thick lava flows and domes.

Pumice

Light-colored, porous igneous rock resulting from explosive volcanic eruptions.
Often has a frothy texture due to gas bubbles trapped during cooling.

Obsidian

Volcanic glass formed from rapid cooling of felsic lava.
Characterized by its glassy texture and often dark color.

Granite

Light-colored igneous rock with visible grains.
Composed mainly of quartz, feldspar, and minor minerals.
Forms from slow crystallization of magma beneath the surface.

Country Rock

Refers to the native rock surrounding plutons.
Intrusive bodies like dikes can intersect and alter country rock.

Contact Metamorphism

Occurs when a rock's mineralogy and texture change due to heat and pressure from nearby molten magma.

Felsic Rocks

Rich in quartz and feldspar, typically lighter in color.
Common felsic minerals include quartz and muscovite.

Mafic Rocks

Rich in magnesium and iron, usually darker in color.
Common mafic minerals include olivine, pyroxene, and biotite.

Feldspar

Constitutes over half of the Earth's crust.
Formed from aluminum, silica, oxygen, and potassium combinations.

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Description

Explore the fascinating world of igneous rocks with this flashcard quiz. Understand the formation of both igneous and intrusive rocks, their characteristics, and their origins. Perfect for geology enthusiasts or students studying Earth science!