Many diorites are truly igneous, having crystallized from molten material (magma). The chemical composition of diorite is intermediate between gabbro and granite. Diorite is usually grey to dark grey in colour, but it can also be black or bluish-grey, and frequently has a greenish cast. Granite is the most common type of land based intrusive rock, while gabbro is the type found most often underwater. What are Igneous Rocks – Intrusive and Extrusive Igneous rocks are rocks that are created beneath the earth in the earths mantle or above on the earth’s surface. Intrusive rocks are formed from magma that cools and solidifies within the crust of the planet. Examples include basalt, rhyolite, andesite, and obsidian. Intrusive. Igneous rocks with similar composition are basalt (extrusive equivalent of gabbro) and diabase (the same rock type could be named dolerite or microgabbro instead). We can tell the difference between intrusive and extrusive rock by noticing the texture of the rock surface. This makes it difficult to carve and work with, but also allows it to be worked finely and take a high polish, and to provide a durable finished work. The presence of sodium-rich feldspar, oligoclase or andesine, in contrast to calcium-rich plagioclase, labradorite or bytownite, is the main distinction between diorite and gabbro . Diorite has a phaneritic, often speckled, texture of coarse grain size and is occasionally porphyritic. Geology Victoria Map 1553A. 3. Intrusive Igneous Rock Photos . [3] Minor amounts of muscovite may also be present. They represent the plutonic rocks formed as a result of differentiation of the MORB magma that fed the volcanic activity along the rift. Felsic: Derived from the words feldspar and silica to describe an igneous rock having abundant light-colored minerals such as quartz, ... Diorite is a classic "salt and pepper" rock with a phaneritic texture. In rapidly cooling magma, the resulting grains and crystals that form the rock are tiny in contrast to the larger grains and crystals found in rocks that cooled much slower deep in the crust. The presence of sodium-rich feldspar, oligoclase or andesine, in contrast to calcium-rich plagioclase, labradorite or bytownite, is the main distinction between diorite and gabbro. 2 marks Cooled slowly because magma or lava are formed cooled slowly and the mineral has time to grow and form large crystals. Andesite (Extrusive) 6 years ago ... Pictures of Intrusive and Extrusive Igneous Rocks . diorite Diorite is an intrusive plutonic rock with a composition that is intermediate between gabbro and granite. Most intrusive rocks are coarse grained and exhibit no spaces or air pockets. Our editors will review what you’ve submitted and determine whether to revise the article. Extrusive Igneous Rock. Intrusive rocks form plutons and so are also called plutonic. The chemical composition of diorite is intermediate, between that of mafic gabbro and felsic granite. Diorite has about the same structural properties as granite but, perhaps because of its darker colour and more limited supply, is rarely used as an ornamental and building material. The large interlocking crystal grains indicate slow cooling deep below the earth's surface; Aphanitic texture -- basalt: This is a volcanic (or extrusive) igneous rock. Phaneritic texture-- granite: This is a plutonic (or intrusive) igneous rock. Basalt is an extrusive or intrusive rock that makes up most of the world's oceanic crust. Diorite, medium- to coarse-grained intrusive igneous rock that commonly is composed of about two-thirds plagioclase feldspar and one-third dark-coloured minerals, such as hornblende or biotite. (1980). There are five types of intrusive rocks, which are granite, pegmatite, gabbro, diorite and peridotite. The two main categories of igneous rocks are extrusive and intrusive. Andesite can be considered as the extrusive equivalent of plutonic diorite. Diorite (Intrusive) 6 years ago. Let us know if you have suggestions to improve this article (requires login). Basalt (Extrusive) 6 years ago. OBSIDIAN Obsidian is an extrusive volcanic rock formed by the rapid cooling of high viscosity magma. Gabbro with large augite phenocrysts embedded in … Basalt. It is one of the dark gray stones that is sold commercially as black granite. The chemical composition of diorite is intermediate, between that of mafic gabbro and felsic granite. It is recognized by its glassy texture. This article was most recently revised and updated by, https://www.britannica.com/science/diorite, Amethyst Galleries' Mineral Gallery - Diorite. These rocks usually form from a volcano, so they are also called volcanic rocks. By signing up for this email, you are agreeing to news, offers, and information from Encyclopaedia Britannica. Dacite (Extrusive) 6 years ago. Updates? Diorite ( /ˈdaɪ.əˌraɪt/[1][2]) is an intrusive igneous rock composed principally of the silicate minerals plagioclase feldspar (typically andesine), biotite, hornblende, and/or pyroxene. The chemical composition of diorite is intermediate between gabbro and granite. It is commonly produced in volcanic arcs, and in cordilleran mountain building, such as in the Andes Mountains, as large batholiths. Lava that is released by volcanoes and felsic granite and extrusive igneous are!, the cooling proceeds slowly texture of coarse grain size and is occasionally porphyritic are also called rocks. Size and is occasionally porphyritic can be considered as the extrusive equivalent of diorite is intermediate gabbro. Above the surface of the planet of diorite is intermediate between gabbro and felsic.! 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