Ch. 4: Igneous Rocks

Geology 1330 with Lytwyn at University of Houston - main campus

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By: Jenn McCaskill
Created: 2011-04-15
Size: 63 flashcards
Views: 98

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Andesitic

intermediate composition:

Aphanitic texture

texture of igneous rocks in which crystals are too small for minerals to be individually distinguished without the aid of a microscope

Assimilation

the process of incorporating country rock into a magma body

Bowens reaction series

A concept that illustrates the relationships between magma and the minerals crystallizing from it during the formation of igneous rocks

Crystallization

formation or growth of a crystalline solid from a liquid or a gas

Crystal settling

during the crystallization of magma, the earlier formed minerals are denser than the liquid portion and settle to he bottom of the magma chamber

Extrusive

Igneous activity that occurs at the Earth's surface

Decompression melting

melting that occurs as a rock ascends due to a drop in confining pressure

Felsic

Granitic composition: compositional group of igneous rocks indicating that the rock is composed almost entirely of light-colored silicates

Pyroclastic

composed of fragments ejected during a volcanic eruption

Glass

Natural glass that forms when molten lava cools too rapidly to recrystallize; solid composed of unordered atoms

Glassy texture

Describes certain igneous rocks, like obsidian, that contain no crystals

Groundmass

The matrix of smaller crystals within an igneous rock that has porphyritic texture

Granitic

compositional group of igneous rock indicating the rock is composed almost entirely of light-colored silicates

Intermediate

compositional group of igneous rocks, indicating the rock contains at least 25% dark-silicate minerals. The other dominant mineral is plagioclase feldspar

Intrusive

Igneous rocks that formed beneath Earth's surface

Lava

Magma that reaches earth's surface

Mafic

Basaltic composition

Magma

A body of molten rock found at depth, including any dissolved gases and crystals

Magma mixing

the process of altering the composition of a magma through the mixing of a material from another magma body

Melt

The liquid portion of magma excluding the solid crystals

Partial melting

The process by which most igneous rocks melt. Individual minerals have different melting points- igneous rocks melt over a range of a few hundred degrees; if liquid is squeezed out after melting has occurred, a melt w/ a higher silica content results

Phaneritic texture

igneous rock texture in which the crystals are roughly equal in size and large enough so the individual minerals can be identified without aid of a microscope

Magmatic differentiation

process of generating more than one rock type from a single magma

Phenocryst

Conspicuously large crystal embedded in a matrix of finer-grained crystals

Plutonic

igneous rocks that form at depth,

Porphyritic texture

an igneous rock texture characterized by two distinctively different crystal sizes. the larger crystals are called phenocrysts and matrix of smaller crystals is called groundmass

Ultramafic

compositional group of igneous rocks containing mostly olivine and pyroxene

Vesicular texture

a term applied to aphanitic igneous rocks that contain only small cavities called vesicles

Volatiles

Gaseous components of magma dissolved in the melt. Will readily vaporize (from a gas) at surface pressures

Volcanic

Pertaining to the activities, structures, or rock types of a volcano

Rhyolite

Felsic

may contain glass fragments and vesicles

aphanitic texture

mostly quartz and potassium feldspars

Granite

Phaneritic

Over 25% quartz and 65% feldspars

May contain biovite and muscovite mica

Very abundant- mountain building

Andesite

volcanic origin

intermediate

aphanitic or porphyritic texture

amphibole and intermediate feldspar

Diorite

plutonic equivalent of andesite

intermediate

coarse grained

Basalt

mafic

volcanic

aphanitic

composed of pyroxene and calcium-rich plagioclase feldspar

most common extrusive igneous rock

Gabbro

intrusive equivalent of basalt

phaneritic- pyroxene and calcium-rich plagioclase feldspar

significant % of oceanic crust

mafic

Peridotite

ultramafic

ferromagnesian minerals

main rock of upper mantle

Pumice

frothy glass texture

formed from lava rich in gas bubbles

Obsidian

compact glass texture

formed from lava without gases

dense

Volcanic tuff

Pyroclastic rock made of ash-sized fragments

Volcanic breccia

pyroclastic rock made of particles larger than ash

Which of the following igneous rocks has a pyroclastic texture

rhyolitic tuff

The sizes, shapes, and arrangements of mineral grains in an igneous rock is known as _____________

texture

Changing the composition of magma by incorporating surrounding host rock is known as __________

assimilation

T/F Olivine and quartz commonly crystallize together from mafic or basaltic magmas

FALSE

Which igneous rock or magma has the lowest silica content?

basalt

Lava flows are typically finer grained than intrusive rocks. Why?

The extrusive magma cools quickly so the mineral grains do not have time to grow

T/F A feldspar crystal where a calcium rich interior is surrounded by a sodium rich rim indicates that there was incomplete reaction between the crystal and surrounding magma

TRUE

T/F Andesitic magma can form through differentiation of granitic magma

FALSE

Consider Bowen's reaction series. Which mineral would you expect to see as a phenocryst in a porphyritic basalt?

Olivine

What texture describes an igneous rock that has two or more distinctly different-sized populations of mineral grains?

Porphyritic

Which of the following igneous rocks has a phaneritic texture?

Gabbro

T/F The formation of a secondary magma of different composition from a parent magma is called magmatic differentiation

TRUE

What type of magma, commonly erupted along oceanic ridge systems, originates by partial melting of mantle peridotite?

Basalt

Which of the following pairs of igneous rocks have the same composition?

Rhyolite and granite

What is the name of a volcanic rock that is extremely vesicular and glassy?

Pumice

All of the following are factors that affect the generation of magma except for _____________

crystal size

__________ is thought to be common in the Earth's mantle but rare in the crust.

Peridotite

factors or processes that influence the composition of magma

-Composition of the original rock that melted to form the magma

-Types of minerals that crystallize from magma

-Mixing of magmas having different compositions
-Composition of any host rock assimilated by the magma

On the basis of Bowen's reaction series, which of the following minerals has the lowest melting temperature?

Quartz

T/F Dry basalt melts at a higher temperature than dry granite

TRUE

Decompression melting in the generation of magma is common along...

Mid-ocean ridges

About this deck

By: Jenn McCaskill
Created: 2011-04-15
Size: 63 flashcards
Views: 98

About StudyBlue

“I have been getting MUCH better grades on all my tests for school. Flash cards, notes, and quizzes are great on here. Thanks!”
Kathy