A laccolith is an igneous intrusion (or concordant pluton) that has been injected between two layers of sedimentary rock. The pressure of the magma is high enough that the overlying strata are forced upward, giving the laccolith a dome or mushroom-like form with a generally planar base. Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... Pluton redirects here. ... Two types of sedimentary rock: limey shale overlaid by limestone. ... Magma is molten rock located beneath the surface of the Earth (or any other rocky planet), and which often collects in a magma chamber. ...

Laccoliths tend to form at relatively shallow depths and are typically formed by relatively viscous magmas, such as those that crystallize to diorite, granodiorite, and granite. Cooling underground takes place slowly, giving time for larger crystals to form in the cooling magma. The surface rock above laccoliths often erodes away completely, leaving the core mound of igneous rock. The term was first applied as laccolite by Grove Karl Gilbert after his study of intrusions of diorite in the Henry Mountains of Utah in about 1875. Categories: Mineral stubs | Igneous rocks ... Granodiorite is an intrusive igneous rock similar to granite, but contains more plagioclase than potassium feldspar. ... Quarrying granite for the Mormon Temple, Utah Territory. ... Grove, Karl, Gilbert (May 6, 1843 – May 1, 1918), known by the abbreviated name in academic literature, was an American geologist. ... Categories: Mineral stubs | Igneous rocks ... An image of peaks in the Henry mountains viewed from a high mountain road. ...

It is often difficult to reconstruct shapes of intrusions. For instance, Devils Tower in Wyoming was proposed to be the remnants of an ancient laccolith. The rock would have had to cool very slowly so as to form the slender pencil-shaped columns of phonolite porphyry seen today. At Devils Tower, however, erosion has stripped away the overlying and surrounding rock, and so it is impossible to reconstruct the original shape of the igneous intrusion; that rock may not be the remnant of a laccolith. At other localities, such as in the Henry Mountains and other isolated mountain ranges of the Colorado Plateau, some intrusions domonstrably have shapes of laccoliths. The small Barber Hill syenite-stock laccolith in Charlotte, Vermont USA, has several volcanic trachyte dikes associated with it. Molybdenite is also visible in outcrops on this exposed laccolith. Devils Tower National Monument Devils Tower is a geological feature located in eastern Wyoming that was established as the first United States National Monument in 1906. ... This article does not cite its references or sources. ... Phonolite is an igneous, volcanic (extrusive) rock, of felsic composition, with aphanitic to porphyritic texture. ... Porphyry is a very hard igneous rock consisting of large-grained crystals, such as feldspar or quartz, dispersed in a fine-grained feldspathic matrix or groundmass. ... Devils Tower National Monument Devils Tower is a geological feature located in eastern Wyoming that was established as the first United States National Monument in 1906. ... An image of peaks in the Henry mountains viewed from a high mountain road. ... The Colorado Plateau, also called the Colorado Plateaus Province, is a physiographic region of the Intermontane Plateaus, roughly centered on the Four Corners region of the southwestern United States. ... Syenite Syenite is a coarse-grained intrusive igneous rock of the same general composition as granite but with the quartz either absent or present in relatively small amounts. ... Trachyte is an igneous, volcanic rock with an aphanitic to porphyritic texture. ...

See also

• Batholith
• Dike
• Sill