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| Igneous rocks having a mineral makeup between that of granite and basalt, after the common volcanic rock andesite. |
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| A texture of igneous rocks in which the crystals are too small for individual minerals to be distinguished with ther unaided eye. |
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| As magma migrates upward, it may incorporate some of the surrounding host rock. |
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| Term used to describe igneous rocks that contain abundant dark minerals and about 50 percent silica. |
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| A concept proposed by N.L. Bowen that illustrates the relationship between magma and the minerals crystallizing from it during the formation of igneous rock. |
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| The formation and growth of a crystalline solid from a liquid or gas. |
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| This process occurs when the earlier-formed minerals are denser that the liquid portion and sink toward the bottom of the magma chamber. |
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Melting that occurs as rock ascends due to a drop in confining pressure. |
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| Igneous activity that occurs at Earth's surface. |
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| A term derived from feldspar and silica. It is a term used to describe granitic igneous rocks. |
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| Fragmental/Pyroclastic Texture |
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Definition
| An igneous rock texture resulting from the consolidation of individual rock fragments that are ejected during a violent eruption. |
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| The gradual increase in temperature with depth in the crust. The average is 30 degrees celcius per kilometer in the upper crust. |
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| Natural glass produced when molten lava cools too rapidly to permit crystalization. Volcanic glass is a solid composed of unordered atoms. |
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| A term used to describe the texture of certain igneous rocks, such as obsidian, that contain no crystals. |
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| The matrix of smaller crystals within an igneous rock that has porphyritic texture. |
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| Igneous rocks composed mainly of light-colored silicates are said to have this composition. |
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| Chemical alterations that occur as hot, ion-rich water circulates through fractures in rock. |
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| Rocks formed by the crystallization of molten magma. |
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| Intermediate/Andesitic Composition |
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| Rocks with a composition between granitic and basaltic rocks. |
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| Igneous rock that formed below Earth's surface. |
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Magma that reaches Earth's surface. |
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| Because basaltic rocks contain a high percentage of ferromagnesian minerals, they are also called mafic. |
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| A body of molten rock found at depth, including any dissolved gases and crystals. |
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| One magma body intrudes another. |
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| The formation of one or more secondary magmas from a single parent magma. |
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| The liquid portion of magma excluding the solid crystals. |
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| The process by which most igneous rocks melt. Because individual minerals have different melting points, most igneous rocks melt over a temperature range of a few hundred degrees. If the liquid is squeezed out after some melting has occured, a melt with a higher silica content results. |
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| A very coarse-grained igneous rock 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. |
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| A texture of igneous rocks in which the interlocking crystals are all larger than one centimeter in diameter. |
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| An igneous rock texture in which the crystals are roughly equal in size and large enough so that individual minerals can be identified with the unaided eye. |
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| Conspicuously large crystals in a porphyry that are imbedded in a matrix of finer-grained crystals. |
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| Igneous rocks that form at depth are termed intrusive or plutonic. |
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| An igneous rock texture characterized by two distinctively different crystal sizes. The larger crystals are called phenocrysts, and the matrix of smaller crystals is termed the groundmass. |
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Definition
| An igneous rock with a porphyritic texture. |
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Definition
| An igneous rock texture resulting from the consolidation of individual rock fragments that are ejected during a violent eruption. |
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| The size, shape, and distribution of the particles that collectively constitute a rock. |
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| Compositional category for igneous rocks made up almost entirely of ferromagnesian minerals. |
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| A term applied to aphanitic igneous rocks that contain many small cavities, called vesicles. |
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| Gaseous components of magma dissolved in the melt. Volatiles will readily vaporize at surface pressures. |
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| Pertaining to the activities, structures, or rock types of a volcano. |
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