Whereas plutonic rocks form continents, basalt lies in the crust underneath the oceans. Intrusive rocks are formed when magma cools underneath Earth’s surface. Dark colored diabase dikes intrude through light colored granite at Acadia National Park, Maine. 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. basalt-exrusive obsidian-extrusive pumice-extrusive granite-Intrusive Extrusive means its on the surface (on the ground). Coarse grained. 4a, b). Figure 4. Properties of Igneous Rocks. Pyroxene, Amphibole, possibly Biotite and/or Olivine. 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. Basaltic Glass. Felsic. Quartz, Potassium-Felspar, Plagioclase Fledspar, Biotite Mica & Amphibole ... Diabase. 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. 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. Extrusive igneous rocks erupt onto the surface, where they cool quickly to form small crystals. can be intrusive or extrusive Can be fine or coarse grained* mafic. Greater then 95% of Diabase is composed of 2 minerals. It is equivalent in composition to the coarse grained intrusive rock Gabbro and to the fine grained extrusive rock Basalt.. 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. 2 Extrusive igneous rocks. Intrusive Igneous Rock . Intrusions are formed inside country rock which prevents the magma (=molten rock) intrusion from cooling quickly. 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.

Figure 01: Igneous Rock. Extrusive rocks have very small, almost microscopic crystals. NPS photo by Georgia Hybels. Each kind of texture has a variety of different characteristics that make them unique. Intrusive, or plutonic, igneous rock forms when magma remains inside the Earth's crust where it cools and … Intrusive. Examples of intrusive igneous rocks are diorite, gabbro, granite, pegmatite, and peridotite. The Jurassic age York Haven Type Diabase is what forms the Monocacy Hill intnlsion. See igneous rocks are classified into extrusive and intrusive categories. Its principal minerals are feldspars, quartz, and mica. 1. Extrusive. Preliminary QAPF classification of: a – intrusive rocks; b – extrusive rocks. Intrusive igneous rocks crystallize below Earth's surface, and the slow cooling that occurs there allows large crystals to form. Non-vesicular. Diabase: A hand specimen of diabase approximately ten centimeters across. Basalt Igneous rock Composition Mafic: plagioclase, amphibole, and pyroxene, sometimes feldspathoids, or olivine. Surrounded by pre-existing rock (called country rock), the magma cools slowly, and as a result these rocks are coarse grained. Extrusive… This rock's name (Diabase) is defined by it's medium grained size crystals. (after Le Maitre, 2005) Once you have determined the mineral assemblage of a rock, you can use the appropriate (intrusive or extrusive) QAPF chart to name it (fig. These types of rock include diabase, quartz-dolerite, micro-granite and diorite.