Alkali feldspar: Group of silicate minerals that include Albite (NaAlSi3O8) and Orthoclase (KalSi3O8).
Andesite: Fine-grained extrusive igneous rock composed of intermediate composition.
Aphanitic: Texture of igneous rocks where the crystal size cannot be seen. Denotes a rock that has cooled quickly.
Basalt: Fine-grained extrusive igneous rock of basic composition.
Basic: Classification of igneous rock that contains between 45 and 52 percent silica.
Breccia: Volcanic ash that has cooled and solidified that contains large (>2 mm) fragments in a fine-grained matrix.
Diorite: Coarse-grained intrusive igneous rock of intermediate composition.
Extrusive igneous rocks: Igneous rocks that formed by the flow of lava or deposition of ash over preexisting surfaces.
Gabbro: Coarse-grained intrusive igneous rock of basic composition.
Granite: Coarse grained intrusive igneous rock of acidic composition.
Igneous rocks: Rocks formed by solidification from a molten state.
Intermediate: Classification of igneous rock that contains between 52 and 66 percent silica.
Intrusive igneous rocks: Igneous rocks that formed from magma that has solidified in preexisting rock beneath the surface of the earth.
Lava: Rock that is in a molten state, always at the surface.
Magma: Rock that is in a molten state, generally at depth.
Obsidian: Type of igneous rock that is of a glassy texture.
Olivine: Pale green to dark green silicate mineral with the composition of (Mg, Fe)2SiO4.
Pegmatite: Type of igneous rock, coarse-grained, generally of acidic composition. Occasionally contains rare minerals, such as diamonds.
Peridotite: Coarse-grained ultrabasic rock composed of mostly olivine and pyroxene.
Phaneritic: Texture of igneous rocks where the crystal size can bee seen. Denotes a rock that has cooled slowly.
Plagioclase feldspar: Group of silicate minerals that include Albite (NaAlSi3O8) and Anorthite (CaAl2Si2O8)
Porphyritic: Texture of igneous rocks where large crystals are surrounded by a fine-grained matrix. Represents a rock that started out cooling slowly and then cooled rapidly.
Pyroxene: Group of silicate minerals divided into three series and includes such minerals as Hypersthene (Mg, Fe) SiO3, Diopside CaMgSi2O6, and Jadeite NaAlSi2O6.
Rhyolite: Fine-grained extrusive igneous rock of acidic composition.
Tuff: Volcanic ash that has cooled and solidified.
Ultrabasic: Classification of igneous rock that contains less than 45 percent silica.
The copyright of the article Igneous Rocks - Page 3 in Everyday Geology is owned by . Permission to republish Igneous Rocks - Page 3 in print or online must be granted by the author in writing.
