Chapter 3- Igneous Rocks and Intrusive Activity

Obsidian

- dark-colored glassy rock. Metallic ions. Felsic

Laccoliths

Igneous intrusions that can lift the sedimentary strata they penetrate, creating arched beds of sedimentary rock.

crystallization

In the process of _____, cooling reverses the events of melting. As the temperature of the liquid drops, ions pack more closely together as their rate of movement slows. When cooled sufficiently, the forces of the chemical bonds will again confine the ions to an orderly crystalline arrangement.

Gabbro

Intrusive equivalent of basalt. Uncommon in continental crust; significant percentage in oceanic crust. Mafic

felsic

Minerals with granitic composition are almost entirely light-colored silicates- quartz and feldspar. Geologists also call these types of rocks ____, a term derived from feldspar and silica.

assimilation

Once a magma body is formed its composition can still change through the incorporation of foreign material known as ____.

ultramafic

Peridotite contains mostly olivine and pyroxene and thus falls on the opposite side of granitic rocks. It is composed almost entirely of ferromagnesian minerals making geologists refer to it as ____.

glass

Rocks that consist of unordered ions that are "frozen" randomly in place are referred to as ____.

mafic

Rocks that contain substantial dark silicates minerals and calcium-rich plagioclase feldspar (but no quartz) are said to have a basaltic composition, which means they contain a high percentage of ferromagnesian minerals, so geologists also refer to them as ____.

andesitic

Rocks with intermediate composition or ____ composition fall between granitic and basaltic. This type of rock is generally confined to the margins of the continents.

Stocks

Similar to batholiths in composition, but smaller in size.

volatiles

The gaseous components of magma, called ____, are materials that will vaporize (from a gas) at surface pressures. The most common are water vapor, carbon dioxide, and sulfur dioxide.

partial melting

The incomplete melting of rocks is known as ____.

melt

The liquid portion of magma, called ____, is composed mainly of mobile ions of the eight most common elements in the earth's crust- silicon and oxygen, along with lesser amounts of aluminum, potassium, calcium, sodium, iron, and magnesium.

intrusions

The structures that result from the emplacement of magma into preexisting rocks are called plutons or ____.

Basalt

Very dark green to black, aphanitic rock. Most common extrusive rock. Mafic

Welded tuff

When particles remain hot enough to fuse, they are called welded tuff. ____ blankets portions of formerly active volcanic areas.

Phaneritic

____ (coarse-grained) texture- rocks that form in large masses of magma that slowly crystallize. Intrusive

Aphanitic

____ (fine-grained) texture- rocks that formed at the surface, or as small intrusive masses within the upper crust where cooling is relatively rapid. Rocks that have voids left in the rock, caused by gas bubbles are said to have vesicular texture.

Pyroclastic

____ (fragmental) texture- rocks ejected from a violent eruption that resemble a very fine ash, molten blobs, or large angular blocks torn from the walls of the vent during the eruption.

Columnar joints

____ form as igneous rocks cool and develop shrinkage fractures that produce elongated, pillar-like columns.

Intrusive

____ igneous rocks form when magma loses its mobility before reaching the surface, eventually crystallizing. (A.k.a. plutonic rocks)

Extrusive

____ igneous rocks form when molten rock solidifies at the surface. (A.k.a. volcanic rocks)

Magma mixing

____ occurs when one magma body intrudes another that has a different composition.

Bowen's reaction series

____ shows the sequence in which minerals crystallize from a magma.

Pegmatitic

____ texture- rocks that form with unusually large crystals toward the end of crystallization. There is a higher concentration of volatiles that enhance the melt. Intrusive

Porphyritic

____ texture- rocks that have large crystals embedded in a matrix of smaller crystals. The large crystals are called phenocrysts and the smaller crystals are called groundmass. Extrusive.

Glassy

_____ texture- rocks ejected into the atmosphere, where it is quenched rapidly. It is characterized by unordered ions being "frozen in place" before they unite into an orderly crystalline structure. Intrusive.

Granite

composed of 25% Quartz; 65% feldspar. Very abundant rock. Coarse-grained. Felsic

Dikes

discordant bodies that cut across bedding surfaces or other structures in the host rock.

Rhyolite

extrusive equivalent of granite. Composed of essentially the same minerals as Granite. Fine grained. Pink. Felsic

Diorite

intrusive version of andesite. Salt and pepper appearance. andesitic

Andesite

medium-gray, fine-grained rock. andesitic

Sills

nearly horizontal, concordant bodies that form when magma exploits weaknesses between sedimentary beds.

Texture

term used to describe the overall appearance of a rock based in the size, shape, and arrangement of its mineral grains. Three factors that influence the _____ of igneous rocks: The rate at which molten rock cools, the amount of silica present, the amount of dissolved gases in the magma.

Hydrothermal solutions

the hot, watery solution that escapes from a mass of magma during the latter stages of crystallization. Such solutions may alter the surrounding country rock and are frequently the source of significant ore deposits.

Batholiths

the largest igneous body. Almost always made of felsic and intermediate rock types. Must be greater than 100 square kilometers.

Magma

the parent material for igneous rocks. If this molten magma reaches the surface, it is called lava. Most consist of three distinct parts- a liquid component, a solid component, and a gaseous phase.

Crystal settling

the process that occurs when the earlier-formed minerals are more dense than the liquid portion and sink toward the bottom of the magma chamber. This may cause the formation of one or more secondary magmas from a single parent magma which is called magmatic differentiation.

Pumice

volcanic rock with a glassy texture and large air-bubbles throughout. Felsic