Chapter 4 Geology Vocab
extrusive igneous rocks
formed at the crust's surface as a result of the partial melting of rocks within the mantle and crust.
intrusive igneous rocks
formed below the Earth's surface
volatiles
gaseous components of magma dissolved in the melt, volatiles readily vaporize at surface pressures
lava
magma that reaches the Earth's surface
glass
natural glass produced when molten lava cools too rapidly to permit recrystallization volcanic glass is a solid composed of unordered atoms
partial melting
process by which most igneous rocks melt since individual minerals have different melting points. Igneous rocks melt over a temperature range of a few hundred degrees. Liquid is squeezed out after some melting and melts with a higher silica content.
magma mixing
process of altering composition of magma through mixing of material from another body
magmatic differentiation
process of generating more than one rock type from a single magma
fragmental texture
pyroclastic texture
igneous rocks
rock formed from the crystallization of magma
concordant
A term used to describe intrusive igneous masses that form parallel to the bedding of the surround rock.
discordant
A term used to describe plutons that cut across existing rock structures such as bedding planes
Bowen's reaction series
Concept proposed by Norman L. Bowen that illustrates relationships between magma and minerals crystallizing during formation of igneous rocks
crystal settling
During crystallization of magma earlier-formed materials are denser than the liquid portion and settle to the bottom of the magma chamber
geothermal gradient
Gradual increase in temperature with depth in the crust. Average 30 degrees Celsius in the upper crust
felsic
Granitic composition
basaltic composition
Group of igneous rocks indicating rock contains substantial dark silicate minerals and calcium-rich plagioclase feldspar
porphyry
Igneous rocks with porphyritic texture
assimilation
In igneous activity the process of incorporating country rock into a magma body
andesitic composition
Intermediate composition
decompression melting
Melting that occurs as rock ascends due to a drop in confining pressure
coarse-grained texture
Phaneritic texture
intrusions
Pluton
aphanitic texture
Texture of igneous rocks in which the crystals are too small for individual minerals to be distinguished without the aid of a microscope
crystallization
The formation and growth of a crystalline solid from a liquid or gas
Pegmatite
Very coarse-grained igneous rock like granite that is found as a dike and is associated with a large mass of plutonic rocks. There are smaller crystals. Bigger crystals crystallize in a rich-water environment
magma
a body of molten rock found at depth, including dissolved gases and crystals
granitic composition
a compositional group of igneous rocks indicating the rock is composed almost entirely of light-colored silicates
intermediate composition
a compositional group of igneous rocks, indicating that the rock contains at least 25% of dark silicate minerals like plagioclase feldspar
stocks
a pluton similar to but smaller than a batholith
Plutons
a structure that results from the emplacement and crystallization of magma beneath the surface of the earth.
sills
a tabular igneous body that was intruded parallel to layering of preexisting rock
massive
an igneous pluton that is not tabular in shape
xenoliths
an inclusion of unmelted country rock in an igneous pluton
fine-grained texture
aphanitic texture
mafic
basaltic composition
Phenocryst
conspicuously large crystal embedded in a matrix of finer-grained crystals.
volcanic rocks
created when rocks are melted through enormous amounts of heat and pressure and liquid magma is forced through other rocks to erupt on Earth's surface as lava
tabular
describing a feature such as an igneous pluton having two dimensions that are much larger than the third
ultramafic
group of igneous rocks containing mostly pyroxene and olivine.
porphyritic texture
igneous rock texture characterized by two distinctively different crystal sizes. The larger crystals are called phenocrystals, whereas the matrix of smaller crystals is termed to groundmass.
phaneritic texture
igneous rock texture in which crystals are roughly equal in size. Large enough so individual minerals can be identified.
pegmatitic texture
igneous rocks interlocking as crystals are all larger than 1 centimeter in diameter
plutonic rocks
igneous rocks that form at depth. Pluto, the god of the lower world in classical mythology.
batholiths
large mass of igneous rock formed when magma was emplaced at depth, crystallized, and subsequently exposed by erosion.
laccoliths
massive igneous body intruded between preexisting strata
groundmass
matrix of smaller crystals within an igneous rock that has porphyritic texture
columnar joints
pattern of cracks that form during cooling of molten rocks to generate columns
pyroclastic texture
rock texture resulting form consolidation of individual rock fragments ejected during volcanic eruption
texture
size, shape, distribution of particles that collectively constitute a rock
dikes
tabular-shaped intrusive igneous feature that cuts through surrounding rock
vesicular texture
term applied to aphanitic igneous rocks contain many small cavities called vesicles.
glassy texture
texture of certain igneous rocks such as obsidian, contains no crystals
melt
the liquid portion of magma excluding the solid crystals