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GEOL 101
Chapter 4 Note Cards
54
Geology
Undergraduate 1
06/11/2012

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Term
Intrusive Igneous Rocks
Definition
Igneous rock that formed below earth's surface.
Term
Andesitic Composition
Definition
A compositional group of ingneous rocks, indicating that the rock contains at least 25% dark silicate minerals. The other dominat mineral is plagioclase feldspar
Term
Aphanitic Texture
Definition
A texture of igneous rocks in which the crystals are too small for individual minerals to be distinguished with out the aid of a microscope
Term
Assimilation
Definition
In agneous activity, the process of incorperating country rock into a magma body
Term
Baslatic Composition
Definition
A compositonal group of igneous rocks indicating that the rock contains substantial dark silicate minerals and calcium-rich plagioclase feldspar
Term
Batholith
Definition
A large mass of igneous rock that formed when magma was emplaved at depth, crystallized, and subsequently exposed by erosion
Term
Bowen's reaction series
Definition
A concept proposed by N.L. Bowen that illistrates the relationship between magma and the minerals crystallizing from in during the formation of igneous rocks
Term
Course-grained texture
Definition
Consist of a mass of intergrown crystals which are roughly equal in size and large enough so that the individual minerals can be identified without the aid of a microscope
Term
Columnar Joints
Definition
Form as igneous rocks cool and develop shrinkage fractures that produce elongated, pillar-like columns
Term
Concordant
Definition
A term used to discribe intrusive igneous masses that form parallel to the bedding of the surrounding rock
Term
Crystallization
Definition
The formation and growth of a crystalline solid from a liquid or gas
Term
Crystal Settling
Definition
During the crystallization of magma, the earlier-formed minerals are denser than the liquid portion and settle to the bottom of the magma chamber
Term
Decompression melting
Definition
Melting that occurs as rock ascends due to a drop in confining pressure
Term
Dikes
Definition
A tabular-shaped intrustive igneous feature that cuts through the surrounding rocks
Term
Discordant
Definition
Term used used to desribe plutons that cut across existing rock structures, such as bedding planes
Term
Extrusive Ingneous Rocks
Definition
Igneous rocks that form when molten rock solidifies at the sruface
Term
Felsic
Definition
Compositional group of igneous rocks indicating that rock is composed almost entirely of light-colored silicates
Term
Fine-grained texture
Definition
A texure of igneous rocks in which the crystals are too small for individual minerals to be distinguished without the aid of a microscope
Term
Fragmental Texture
Definition
An igneous rock texture resulting from the consolidation of individual rock fragments that are ejected during a violent volcanic eruption
Term
Geothermal Gradient
Definition
The gradual increase in temperature with depth in the crust.
Term
Glass
Definition
Natural glass produced when molten lava cools too rapidly to permit recrystallization. Volcanic glass is solid composed of unordered atoms
Term
Glassy Texture
Definition
Texture of certain igneous rocks such as obsidian, that contains no crystals
Term
Groundmass
Definition
The matrix of smaller crystals within an igneous rock that has prophyritic texture
Term
Granitic Composition
Definition
A compostional group of igneous rocks indicating the rock is composed almost entirely of light-colored silicated
Term
Igneous Rocks
Definition
Rock formed from the crystallization of magma
Term
Intermediate Compostion
Definition
A compostional group of igneous rocks, indicating that the rock contains at least 25% dark silicate minerals.
Term
Intrusions
Definition
A structure that results from the emplacement and crystallization of magma beneath the surface of earth
Term
Laccoliths
Definition
Massive igneous body intruded between preexisting strata
Term
Lava
Definition
Magma that reaches earth surface
Term
Mafic
Definition
From magnesium and ferrum, they are typically darker and denser than granitic rocks
Term
Magma
Definition
A body of molten rock found at depth, including any dissolved gases and crystals
Term
Magma Mixing
Definition
Process of altering the composition of a magma through the mixing of material from another magma body
Term
Magmatic differentiation
Definition
Process of generating more than one rock type from a single magma
Term
Massive
Definition
An ingeous pluton that is not tabular in shape
Term
Melt
Definition
The liquid portion of magma excluding the solid crystals
Term
Partial Melting
Definition
Process by which most igneous rocks melt
Term
Pegmatite
Definition
A very coarse-grained ingeous rock commonly found as a dike associated with a large mass of plutonic rock that has smaller crytals
Term
Pegmatitic Texture
Definition
Texture of ingeous rocks in whcih the interlocking crystals are all arger than one centimeter in diameter.
Term
Phaneritic Texture
Definition
Igneous rock texture in which the crystals are roughly equal in size are large enough so the indivual minerals can be identified without the aid of a microscope
Term
Phenocryst
Definition
Conspicuously large crystal embedded in a matrix of finer-grained crystals
Term
Plutonic Rocks`
Definition
ignoeus rocks that form at depth
Term
Plutons
Definition
structure that results from the emplacement and crystallization of magma beaneth the earths surface
Term
Porphyritic texture
Definition
igneous rock texture characterized by two distinctively different crystal sizes.
Term
Porphyry
Definition
igneous rock with a porphyritic texture
Term
Pyroclastic Texture
Definition
igneous rock texture resulting from the consolidation of individual rock fragments that are ejected during an eruption
Term
Sills
Definition
A tabular igneous body that was intruded parallel to the layering of preexisting rock
Term
Stocks
Definition
A pluton similar to but smaller than a batholith
Term
Tabular
Definition
Describing a feature such as an igneous pluton having two dimensions that are much longer than the third
Term
Texture
Definition
The size, shape, and distribution of the particals that collectively constitute a rock
Term
Ultramafic
Definition
A compositional group of igneous rocks containing mostly olivine and pyroxene
Term
Vesicular Texture
Definition
Term applied to aphanitic igneous rocks that contain many small cavities called vesicles
Term
Volatiles
Definition
Gaseous components of magma dissolved in the melt
Term
Volcanic rocks
Definition
Igneous rocks that form when molten rock solidifies at the surface
Term
Xenoliths
Definition
An inclusion of unmelted country rock in an igneous pluton
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