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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 ...
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 contacts are the surfaces between host (or country) rock and an intrusive magmatic body. [3] The older country rock is crosscut by a younger magmatic body. The nature of the intruding body depends on its composition and depth. Common examples are igneous dikes, sills, plutons, and batholiths. Depending on the composition of the magma ...
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.
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
Monzonite is a coarse-grained igneous rock. Such rocks are classified by their relative percentages of quartz, plagioclase, alkali feldspar, and feldspathoid (the QAPF classification). Monzonite is defined as rock having less than 5% quartz in its QAPF fraction and in which alkali feldspar makes up between 35% and 65% of the total feldspar content.
Examples of phaneritic igneous rocks are gabbro, diorite, and granite. Porphyritic textures develop when conditions during the cooling of magma change relatively quickly. The earlier formed minerals will have formed slowly and remain as large crystals, whereas, sudden cooling causes the rapid crystallization of the remainder of the melt into a ...
A layered intrusion is a large sill-like body of igneous rock which exhibits vertical layering or differences in composition and texture. These intrusions can be many kilometres in area covering from around 100 km 2 (39 sq mi) to over 50,000 km 2 (19,000 sq mi) and several hundred metres to over one kilometre (3,300 ft) in thickness. [ 1 ]