Examples of intrusive igneous rocks are diorite, gabbro, granite, pegmatite, and peridotite. These rocks are in many ways similar to other intrusive rocks, but have intermediate grain sizes and textures, generally half way between those found in extrusive and other types of intrusive rocks. Intrusive Igneous Rock . Intrusive igneous rocks crystallize below Earth's surface, and the slow cooling that occurs there allows large crystals to form. Extrusive. Extrusive… Coarse grained. Basaltic Glass. Diabase is composed of plagioclase feldspar (mostly labradorite) and pyroxene ().The crystals that make up dolerite are usually visible to the naked eye, but sometimes porphyritic rocks of basaltic composition with pyroxene and especially plagioclase phenocrysts are also named that way. See igneous rocks are classified into extrusive and intrusive categories. So, an extrusive igneous rock, is in the extrusive category. They contain less than 45 percent silica, and are believed to originate from the mantle. Preliminary QAPF classification of: a – intrusive rocks; b – extrusive rocks. Whereas plutonic rocks form continents, basalt lies in the crust underneath the oceans. These types of rock include diabase, quartz-dolerite, micro-granite and diorite. Extrusive rocks have very small, almost microscopic crystals. Basalt Igneous rock Composition Mafic: plagioclase, amphibole, and pyroxene, sometimes feldspathoids, or olivine. 2 Extrusive igneous rocks. Diabase: A hand specimen of diabase approximately ten centimeters across. Pyroxene, Amphibole, possibly Biotite and/or Olivine. The bottom salt-and-pepper colored portion is a polished surface displaying the plagioclase (white) and pyroxene (black) minerals that make up this specimen of an intrusive igneous rock. Extrusive igneous rocks erupt onto the surface, where they cool quickly to form small crystals. Surrounded by pre-existing rock (called country rock), the magma cools slowly, and as a result these rocks are coarse grained. As an example, a rock with the same composition could be called gabbro if it were plutonic, diabase if it were intrusive, or basalt if it were extrusive. Felsic. The Jurassic age York Haven Type Diabase is what forms the Monocacy Hill intnlsion. Each kind of texture has a variety of different characteristics that make them unique. NPS photo by Georgia Hybels.

Figure 01: Igneous Rock. It is equivalent in composition to the coarse grained intrusive rock Gabbro and to the fine grained extrusive rock Basalt.. This rock's name (Diabase) is defined by it's medium grained size crystals. 4a, b). Intrusive, or plutonic, igneous rock forms when magma remains inside the Earth's crust where it cools and … Intrusions are formed inside country rock which prevents the magma (=molten rock) intrusion from cooling quickly. Greater then 95% of Diabase is composed of 2 minerals. Non-vesicular. basalt-exrusive obsidian-extrusive pumice-extrusive granite-Intrusive Extrusive means its on the surface (on the ground). Figure 4. Basalt is a mafic extrusive igneous rock formed from the rapid cooling of lava rich in magnesium and iron exposed at or very near the surface of a terrestrial planet or a moon. Its principal minerals are feldspars, quartz, and mica. Intrusive. 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