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Because the solid country rock into which magma intrudes is an excellent insulator, cooling of the magma is extremely slow, and intrusive igneous rock is coarse-grained . However, the rate of cooling is greatest for intrusions at relatively shallow depth, and the rock in such intrusions is often much less coarse-grained than intrusive rock ...
Intrusive igneous rocks are classified separately from extrusive igneous rocks, generally on the basis of their mineral content. The relative amounts of quartz, alkali feldspar, plagioclase, and feldspathoid is particularly important in classifying intrusive igneous rocks. [9] [10] Intrusions must displace existing country rock to make room for ...
Intrusive igneous rocks that form near the surface are termed subvolcanic or hypabyssal rocks and they are usually much finer-grained, often resembling volcanic rock. [8] Hypabyssal rocks are less common than plutonic or volcanic rocks and often form dikes, sills, laccoliths, lopoliths , or phacoliths .
Half Dome, a quartz monzonite monolith in Yosemite National Park and part of the Sierra Nevada Batholith. A batholith (from Ancient Greek bathos 'depth' and lithos 'rock') is a large mass of intrusive igneous rock (also called plutonic rock), larger than 100 km 2 (40 sq mi) in area, [1] that forms from cooled magma deep in the Earth's crust.
Phaneritic (phaner = visible) textures are typical of intrusive igneous rocks, these rocks crystallized slowly below Earth's surface. As magma cools slowly the minerals have time to grow and form large crystals. The minerals in a phaneritic igneous rock are sufficiently large to see each individual crystal with the naked eye.
Plutonism is the geologic theory that the igneous rocks forming the Earth originated from intrusive magmatic activity, with a continuing gradual process of weathering and erosion wearing away rocks, which were then deposited on the sea bed, re-formed into layers of sedimentary rock by heat and pressure, and raised again.
These rock types can include: Mangerite: a pyroxene-bearing monzonite intrusive igneous rock; Charnockite: an orthopyroxene-bearing quartz-feldspar rock, once thought to be intrusive igneous, now recognized as metamorphic; Iron-rich felsic rocks, including monzonite and rapakivi granite; Iron-rich diorite, gabbro, and norite
Also called Indianite. A mineral from the lime-rich end of the plagioclase group of minerals. Anorthites are usually silicates of calcium and aluminium occurring in some basic igneous rocks, typically those produced by the contact metamorphism of impure calcareous sediments. anticline An arched fold in which the layers usually dip away from the fold axis. Contrast syncline. aphanic Having the ...