Geology Pg. 119-151

vesicular texture

/these nearly spherical openings are called vesicles, and the rocks that contain them

granitic composition

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

porphyritic texture

An igneous rock texture characterized by two distinctively different crystal sizes. The larger crystals are called phenocrysts, whereas the matrix of smaller crystals is termed the groundmass

aphanitic

Igneous rocks that form at the surface or as small intrusive masses within the upper crust where cooling is relatively rapid exhibit a fined-grained texture

ultramafic

a compositional group of igneous rocks containing mostly olivine and pryoxene

basaltic composition

a compositional group of igneous rocks indicating that the rock contains substantial dark silicate minerals and calcium-rich plagioclase feldspar

intermediate composition

a compositional group of igneous rocks that contains at least 25 percent dark silicate minerals. The other dominant mineral is plagioclase feldspar

bowen's reaction series

a concept proposed by N.L. Bowen that illustrates the relationships between magma and the minerals crystallizing from it during the formation of igneous rock

viscosity

a measure of a fluid's resistance to flow

magma

a parent material for igneous rock that is formed by partial melting that occurs at various levels within Earth's crust and upper mantle to depths of about 250 kms.

porphyry

a rock with a porphyritic texture is termed a_________________.

crystal settling

a separation of various components can occur. this process occurs when earlier-formed minerals are denser (heavier) than the liquid portion and sink toward the bottom of the magma chmaber

felsic

a term derived from feldspar and silica

concordant

a term used to describe intrusive igneous masses that form parallel to the bedding of the surrounding rock

discordant

a term used to describe plutons that cut across existing rock structures, such as bedding planes

pegmatitic texture

a texture of igneous rocks in which the interlocking crystals are all larger than one centimeter in diameter.

pegmatite

a very coarse- grained igneous rock (typically granite) commonly found as a dike associated with a large mass of plutonic rock that has smaller crystals. Crystallization in a water-rich environment is believed to be responsible for the very large crystals

magma mixing

another way the composition of magma can be altered by which the ascent of two chemically distinct magma bodies as the more buoyant mass overtakes the more slowly rising body

dikes

are discordant bodies that cut across beding surfaces or other structures in the country rock

sills

are nearly horizontal, concordant bodies that form when magma exploits weaknesses between sedimentary beds or other structures

assimilation

as magma migrates through the crust, it may incorporate some of the surrounding rock in a process called_______________.

pyroclastic texture or fragmental texture

ejected particles that might be very fine ash, molten blobs, or large angular blocks torn form the walls vent during an eruption. igneous rocks composed of these rock fragments are said to have a_______________, or ________________.

xenoliths

evidence supporting stoping is found in plutons that contains suspended blocks of country rock

volatiles

gaseous components of magma called_________, are materials that vaporize at the surface pressures.

laccoliths

igneous rock forcibly injected between sedimentary strata, so as to arch the beds above while leaving those below relatively flat

volcanic rocks

igneous rocks that form when molten rock solidifies at the surface

tabular or massive

intrusive igneous bodies are generally classified according to their shape as________or__________.

obsidian

is a dark-colored glassy rock that usually forms when highly silica-rich lava cools quickly at earth's surface

andesite

is a medium-gray, fine-grained rock typically of volcanic origin

basalt

is a very green to black, fine grained rock composed primarily of pyroxene and calcium-rich plagioclase feldspar, with lesser amounts of olivine and amphibole

pumice

is a volcanic rock with a glassy texture that forms when large amounts of gas escape through silica-rich lava to generate a gray, frothy mass

melt

is composed mainly of mobile ions of the eight most common elements found in Earth's crust

rhyolite

is the fine-grained equivalent of granite and, like granite, is composed essentially of the light-colored silicates

diorite

is the intrusive equivalent of andesite, it is a coarse-grained rock that looks somewhat like gray granite.

gabbro

is the intrusive equivalent of basalt. it makes up a significant part of the oceanic crust

decompression melting

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

glassy texture

molten rock that is quenched and cooled quickly into a solid.

lava

molten rock that reaches the earth's surface

columnar jointing

occurs when igneous rocks cool and develop shrinkage fractures that produce elongated, pillar like columns that most often have six sides

stocks

smaller plutons are called_______.

mafic

term used for basaltic rocks that contain a high percentage of ferrromagnesian minerals

granite

the best known of all igneous rocks

crystallization

the formation and growth of a crystalline solid from a liquid or ga

magmatic differentiation

the formation of one or more secondary magmas from a single parent magma

geothermal gradient

the gradual increase in temperature with depth in the crust. the average is 30 degrees Celsius per km in the upper crust

partial melting

the incomplete melting of rocks known as_____________, a process that produces most magma.

phenocrysts

the large crystals in porphyritic rocks are referred to as_______________.

batholiths

the largest intrusive igneous bodies

groundmass

the matrix of smaller crystals is called______________.

intrusions or plutons

the structures that result from the emplacement of magma into preexisting rocks

texture

used to describe the overall appearance of a rock based on the size, the shape, and arrangement of its mineral grains

phaneritic

when large masses of magma slowly crystallize at great depth, they form igneous rocks that exhibit a coarse-grained texture

plutonic rocks

when magma crystallizes at depth