Felsic refers to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium.Felsic magma or lava is higher in viscosity than mafic magma/lava.Felsic rocks are usually … Obsidian: felsic Granite: felsic Andesite: intermediate. Andesite: The specimen shown is about two inches (five centimeters) across and has a porphyritic texture. It has less than 10% feldspathoid by volume, with at least 65% of the rock consisting of feldspar in the form of plagioclase. Andesite is classed as an 'intermediate' rock, being halfway The mineral grains in such rocks can generally be recognized with the bare eye. These terms are also used while talking about the characteristics of lava. rocks are basalt and gabbro. When did organ music become associated with baseball? Composition: mafic (enriched in iron and magnesium) Color: black, dark gray or dark brown; Cooling Rate: fast, extrusive; Intrusive Equivalent: gabbro; Other Characteristics: weathers to red-brown, hematite/limonite/clay mixture ANDESITE. Felsic magma, starting much cooler, generally crystallizes before reaching the surface. Typical mafic Andesite usually does not contain olivine. Typical pyroclastic. Due to the color of the minerals forming them, the rocks are either light or dark. Photo by the United States Geological Survey. The formal definition of andesite is problematic. However, none of these classifications are in perfect agreement. Andesite Flow: One of numerous massive andesite flows from the Zarembo Island area of southeastern Alaska. Magma is Earth's most powerful solvent. Who is the longest reigning WWE Champion of all time? This places andesite in the basalt/andesite field of the QAPF diagram. How old was Ralph macchio in the first Karate Kid? Photo by T. Miller, United States Geological Survey. Crystalline rocks with a similar composition include granite and rhyolite. Mafic vs Felsic . Water vapor produced when ocean-floor sediments on an oceanic plate are heated in a subduction zone. Mafic magma is much hotter than felsic magma. Andesite is an extrusive volcanic rock with a composition that is intermediate between basalt and rhyolite. Felsic rocks, on the other hand, are Andesite is typically formed at convergent plate margins but may also occur in other tectonic settings. Slow cooling facilitates the growth of large mineral crystals in the rock. This magma may have received a granitic contribution by melting granitic rocks as it ascended or mixed with granitic magma. Click to explore further. Andesite is INTERMEDIATE in composition between MAFIC and FELSIC rocks. Heat would destroy them. In their study, mafic group B inclusions and, to a lesser extent, group A are stated to be compatible with mafic components of andesite–dacite–rhyolite (ADR) arc-type suites (Whalen et al., 2002, p. 1560) with the stated implications about their petrogenesis under conditions of low pressure, dry melting, and fluxing by hydrous fluids derived from subducted lithosphere. Andesite is a fine-grained rock that forms when the magma erupts onto the surface and crystallizes quickly. The Elusive Definition of Andesite. The best way to learn about rocks is to have specimens available for testing and examination. If it is extrusive, it is a lava flow or pyroclastic? Diorite is a coarse-grained igneous rock that forms when the magma remains below Earth's surface and cools slowly. What is the best way to fold a fitted sheet? Hornblende Andesite Porphyry: A specimen of andesite with large visible hornblende phenocrysts. Because these lavas cooled rapidly at the surface, they are generally composed of small crystals. As iron-rich silicates are normally dark in color, mafic rocks are dark-colored. An example is the hornblende andesite porphyry shown in the accompanying photo. Intermediate lava has a lower silica content than felsic lava, but not as high magnesium or iron levels as found in mafic lava. How do you put grass into a personification? The name of an abundant phenocryst mineral may be used as an adjective to the rock name. If you examine a rock that appears to be andesite, but you are not confident that it meets the mineralogical or chemical classification of andesite, you might properly call it an "andesitoid" rock. The material on this site can not be reproduced, distributed, transmitted, cached or otherwise used, except with prior written permission of Multiply. those that contain alot of ferromagnesian minerals (iron and It means that the rock looks like andesite, but, a microscopic examination or chemical analysis might prove you wrong! Learn vocabulary, terms, and more with flashcards, games, and other study tools. Photo by NASA. Is Obsidian mafic or felsic? No. Extensive felsic lava flows are uncommon, but have travelled as far as 15 km (9.3 mi). The lava flow has a medium viscosity as well, and once cooled, the resulting rock is known as Andesite. The name is derived from the Andes Mountains, as it is a commonly found rock among the mountain chain’s stratovolcanoes. Mafic magma is less viscous than felsic magma. DIORITE - phaneritic rock (large crystals) of both mafic and felsic minerals. Stratovolcanoes: Pavlof Volcano (right) and Pavlof Sister Volcano (left) are a pair of symmetrical stratovolcanoes built of andesite flows and tephra on the Alaska Peninsula. Andesite therefore typically contains a Therefore, more basalt than gabbro, and more granite than rhyolite. Felsic from feldspar (rock) and Silica, it is the silica content which shapes the difference. The mixture of mafic and felsic minerals gives the rock a "salt and pepper" appearance. Gabbro is the name given to intrusive mafic rocks, whereas basalt is the name given to extrusive mafic rocks. Many volcanic plumes and ash eruptions occur when gas-charged andesitic magmas erupt. Mafic lava creates basalt while felsic lava produces andesitic and rhyolite rocks. If that can of beer is shaken and suddenly depressurized by opening the can, the gas and the beer will erupt from the opening. For a fine-grained rock like andesite, these classifications are impossible to use precisely when in the field or the classroom. All Rights Reserved. The mixture of mafic and felsic minerals gives the rock a "salt and pepper" appearance. Intrusive Intrusive igneous rocks are formed from magma that cools and solidifies within the crust of a planet, surrounded by way of pre-present rock (called us of a rock); the magma cools slowly and, as a result, these rocks are coarse-grained. The formal definition of andesite is problematic. For example, it can form at ocean ridges and oceanic hot spots from partial melting of basaltic rocks. These magmas can contain several percent dissolved gas by weight! ANDESITE - aphanitic rock (small crystals) of both mafic and felsic … A rising magma chamber can instantly be depressurized by a landslide, faulting, or other event and an enormous volume of rapidly expanding gas will explode through the overlying rock. Andesite and diorite have a composition that is intermediate between basalt and granite. Posted on August 31, 2014 by triplejunction. 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