Download Intrusive and Extrusive Igneous Rocks

Intrusive and Extrusive Igneous
Rocks
Dana Desonie, Ph.D.
Say Thanks to the Authors
Click http://www.ck12.org/saythanks
(No sign in required)
To access a customizable version of this book, as well as other
interactive content, visit www.ck12.org
CK-12 Foundation is a non-profit organization with a mission to
reduce the cost of textbook materials for the K-12 market both
in the U.S. and worldwide. Using an open-content, web-based
collaborative model termed the FlexBook®, CK-12 intends to
pioneer the generation and distribution of high-quality educational
content that will serve both as core text as well as provide an
adaptive environment for learning, powered through the FlexBook
Platform®.
Copyright © 2014 CK-12 Foundation, www.ck12.org
The names “CK-12” and “CK12” and associated logos and the
terms “FlexBook®” and “FlexBook Platform®” (collectively
“CK-12 Marks”) are trademarks and service marks of CK-12
Foundation and are protected by federal, state, and international
laws.
Any form of reproduction of this book in any format or medium,
in whole or in sections must include the referral attribution link
http://www.ck12.org/saythanks (placed in a visible location) in
addition to the following terms.
Except as otherwise noted, all CK-12 Content (including CK-12
Curriculum Material) is made available to Users in accordance
with the Creative Commons Attribution-Non-Commercial 3.0
Unported (CC BY-NC 3.0) License (http://creativecommons.org/
licenses/by-nc/3.0/), as amended and updated by Creative Commons from time to time (the “CC License”), which is incorporated
herein by this reference.
Complete terms can be found at http://www.ck12.org/terms.
Printed: December 8, 2014
AUTHOR
Dana Desonie, Ph.D.
www.ck12.org
C HAPTER
Chapter 1. Intrusive and Extrusive Igneous Rocks
1
Intrusive and Extrusive
Igneous Rocks
• Compare and contrast intrusive and extrusive igneous rock.
Are these both igneous rocks?
These rocks don’t even look like they’re the same type! They are, at least in the same way that fish and mice are
both vertebrates. They both cooled from magma, but the similarities end there. Can you tell what’s different?
Cooling
Igneous rocks cool from magma. The appearance of the rock is created by the composition of the magma. It is also
determined by the rate that the magma cools. If the magma cools deep underground, it cools slowly. If the magma
cools at or very near the surface, it cools quickly. This results in two different rock types. The rock types can be told
apart by the size of their crystals. The size of the crystals creates the texture of the rock.
Intrusive Igneous Rocks
Intrusive igneous rocks cool underground. Deep in the crust, magma cools slowly. Slow cooling gives crystals a
chance to grow. Intrusive igneous rocks have relatively large crystals that are easy to see. Intrusive igneous rocks
are also called plutonic. A pluton is an igneous rock body that forms within the crust.
Granite is the most common intrusive igneous rock. Pictured below are four types of intrusive rocks ( Figure 1.1).
Geological processes have brought some igneous rocks to the surface. Pictured below is a landscape in California’s
Sierra Nevada Mountains made of granite that has been raised to create mountains ( Figure 1.2).
Extrusive Igneous Rocks
Extrusive igneous rocks form above the surface. The lava cools quickly as it pours out onto the surface ( Figure 1.3).
Extrusive igneous rocks cool much more rapidly than intrusive rocks. The rapid cooling time does not allow time
for large crystals to form. So igneous extrusive rocks have smaller crystals than igneous intrusive rocks. Extrusive
igneous rocks are also called volcanic rocks.
Some extrusive igneous rocks cool so rapidly that crystals do not develop at all. These form a glass, such as obsidian.
Others, such as pumice, contain holes where gas bubbles were trapped in the lava. The holes make pumice so light
1
www.ck12.org
FIGURE 1.1
(A) This granite has more plagioclase
feldspar than many granites.
(B) Dior-
ite has more dark-colored minerals than
granite. (C) Gabbro. (D) Peridotite contains olivine and other mafic minerals.
FIGURE 1.2
California’s Sierra Nevada Mountains are
intrusive igneous rock exposed at Earth’s
surface.
FIGURE 1.3
(A) Lava cools to form extrusive igneous
rock. The rocks here are basalts. (B)
The strange rock formations of Chiricahua
National Monument in Arizona are formed
of the extrusive igneous rock rhyolite.
2
www.ck12.org
Chapter 1. Intrusive and Extrusive Igneous Rocks
that it actually floats in water. The most common extrusive igneous rock is basalt. It is the rock that makes up the
ocean floor. Shown below are three types of extrusive igneous rocks ( Figure 1.4).
FIGURE 1.4
Different cooling rate and gas content resulted in these different textures.
Vocabulary
•
•
•
•
extrusive: Igneous rocks that form at Earth’s surface from rapidly cooling lava.
intrusive: Igneous rocks that form inside the Earth from slowly cooling magma.
pluton: Igneous intrusive rock body that has cooled in the crust.
volcanic rock: Rock that originates in a volcano or volcanic feature.
Summary
• Intrusive igneous rocks cool from magma slowly in the crust. They have large crystals.
• Extrusive igneous rocks cool from lava rapidly at the surface. They have small crystals.
• Texture reflects how an igneous rock formed.
Explore More
Use the resource below to answer the questions that follow.
• Igneous Rocks at http://www.youtube.com/watch?v=deC5af9AW6w (5:06)
MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/58884
3
www.ck12.org
1.
2.
3.
4.
5.
6.
7.
8.
How are intrusive rocks formed?
What size are the crystals in very coarse rocks? Why are they that size?
What are the most common coarse rocks?
How are extrusive rocks formed?
List the three textures for extrusive rocks.
Describe rhyolite.
Describe pumice.
Explain why obsidian appears black.
Review
1. How do intrusive igneous rocks form? What is another name for these rocks?
2. How do extrusive igneous rocks form? What is another name for these rocks?
3. How can you use texture to determine whether an igneous rock is intrusive or extrusive?
References
1. (A) Image copyright MARGRIT HIRSCH, 2013; (B) Image copyright Tyler Boyes, 2013; (C) Mark A. Wilson
(Department of Geology, The College of Wooster); (D) Image copyright Marcin Sylwia Ciesielski, 2013.
Granite, diorite, gabbro, and peridotite are all intrusive igneous rocks. (A, B, D) Used under licenses from
Shutterstock.com; (C) Public domain
2. User:Dcrjsr/Wikimedia Commons. The Sierra Nevada Mountains are made of intrusive igneous rock. CC BY
3.0
3. (A) Courtesy of J.D. Griggs, US Geological Survey; (B) Flickr:SonoranDesertNPS. Lava cools to form
extrusive igneous rock, and rhyolite formations in Chiricahua National Monument. (A) Public Domain; (B)
CC BY 2.0
4. (a) Kevin Walsh (Flickr: kevinzim); (b) User:deltalimatrieste/Wikimedia Commons; (c) Courtesy of the
National Oceanic and Atmospheric Administration. Obsidian, pumice, and basalt are extrusive igneous rocks
that cool at different rates. (a) CC BY 2.0; (b) Public Domain; (c) Public Domain
4