igneous rocks

composition

Igneous rocks are grouped by the size of their crystals and the minerals they contain. The minerals in igneous rocks are grouped into families. Some contain mostly lighter colored minerals, some have a combination of light and dark minerals, and some have mostly darker minerals. The combination of minerals is determined by the composition of the magma. Magmas that produce lighter colored minerals are higher in silica. These create rocks such as granite and rhyolite. Darker colored minerals are found in rocks such as gabbro and basalt. There are actually more than 700 different types of igneous rocks. Diorite is extremely hard and is commonly used for art. It was used extensively by ancient civilizations for vases and other decorative art work (Figure 4.11).

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forming crystals

Igneous rocks form when magma cools and forms crystals. These rocks can form at Earths surface or deep underground. Figure 4.7 shows a landscape in Californias Sierra Nevada that consists entirely of granite. Intrusive igneous rocks cool and form into crystals beneath the surface. Deep in the Earth, magma cools slowly. Slow cooling gives large crystals a chance to form. Intrusive igneous rocks have relatively large crystals that are easy to see. Granite is the most common intrusive igneous rock. Figure 4.8 shows four types of intrusive rocks. Extrusive igneous rocks form above the surface. The lava cools quickly as it pours out onto the surface (Figure

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instructional diagrams

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questions

Which term describes igneous rocks that crystallize above the crust

-->  a. extrusive

b. intrusive

c. magma

d. lava

Which mineral is the most common in a dark-colored, mafic igneous rock?

a. diamond

b. quartz

c. pyroxene

-->  d. olivine

The color of minerals in an igneous rock is determined by

-->  a. the composition of the magma

b. the length of time it took the magma to cool

c. whether it cooled from a lava or a magma

d. none of the above.

An igneous rock with large crystals cooled

a. rapidly from a lav

b. rapidly beneath the surface.

-->  c. slowly from a magma.

d. unknown. It is not possible to tell the rate of cooling from the crystal size.

Extrusive igneous rocks

a. are common because large mountain ranges are made entirely of basalt

-->  b. are common because the seafloor is made up of basalt

c. are rare because not much rock melts to produce lava.

d. are rare because much more magma cools intrusively.

The layer of Earth called the mantle is made entirely of igneous rock.

-->  a. true

b. false

Rock on the ocean floor is intrusive igneous rock.

a. true

-->  b. false

The Sierra Nevada Mountains in California are composed mainly of granite.

-->  a. true

b. false

A basalt looks light colored partly because its crystals are too small to see.

a. true

-->  b. false

When melted rock cools more slowly, it forms larger crystals.

-->  a. true

b. false

Volcanic rock may have so many gas bubbles that it can float on water.

-->  a. true

b. false

Melted rock cools more quickly underground than on Earths surface.

a. true

-->  b. false

Obsidian forms when magma cools and forms crystals.

a. true

-->  b. false

Granite and rhyolite are high silica rocks.

-->  a. true

b. false

Pumice contains holes because gas bubbles were trapped in lava as it cooled.

-->  a. true

b. false

Mountain ranges can be made mainly of igneous rocks.

-->  a. true

b. false

Igneous rock is too hard to be used for art works.

a. true

-->  b. false

Basalt crystals are too small to see with the unaided eye.

-->  a. true

b. false

The combination of minerals in igneous rocks is determined by the composition of the magma or lava.

-->  a. true

b. false

Both porphyry and diorite are extrusive igneous rocks.

-->  a. true

b. false

any rock that forms when magma or lava cools

a. extrusive igneous rock

b. basalt

-->  c. igneous rock

d. intrusive igneous rock

e. obsidian

f. pumice

g. granite

most common intrusive igneous rock

a. extrusive igneous rock

b. basalt

c. igneous rock

d. intrusive igneous rock

e. obsidian

f. pumice

-->  g. granite

type of igneous rock that forms on Earths surface

-->  a. extrusive igneous rock

b. basalt

c. igneous rock

d. intrusive igneous rock

e. obsidian

f. pumice

g. granite

igneous rock that is full of holes

a. extrusive igneous rock

b. basalt

c. igneous rock

d. intrusive igneous rock

e. obsidian

-->  f. pumice

g. granite

most common extrusive igneous rock

a. extrusive igneous rock

-->  b. basalt

c. igneous rock

d. intrusive igneous rock

e. obsidian

f. pumice

g. granite

type of igneous rock that forms beneath Earths surface

a. extrusive igneous rock

b. basalt

c. igneous rock

-->  d. intrusive igneous rock

e. obsidian

f. pumice

g. granite

glass-like igneous rock that does not contain mineral crystals

a. extrusive igneous rock

b. basalt

c. igneous rock

d. intrusive igneous rock

-->  e. obsidian

f. pumice

g. granite

Igneous rocks are classified by

a. the size of their crystals.

b. the type of sediments they contain.

c. their mineral composition.

-->  d. two of the above

How many different kinds of igneous rocks are there?

a. only 7

b. about 70

-->  c. more than 700

d. between 70 and 100

Granite is used to make

a. countertops.

b. buildings.

c. statues.

-->  d. all of the above

How is pumice used?

a. to smooth rough skin

b. to stonewash jeans

c. to make vases

-->  d. two of the above

The rock that makes up the ocean floor is

a. granite.

-->  b. basalt.

c. diorite.

d. peridotite.

One property of pumice is

a. a smooth glassy texture.

b. very large crystals.

-->  c. the ability to float on water.

d. none of the above

Many mountain ranges are made of

-->  a. granite.

b. gabbro.

c. andesite.

d. komatite.

diagram questions

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