It is a very common product of regional metamorphism which is associated with mountain building episodes (such rocks are often lineated or foliated because mountain building is a dynamic event that involves motion). Granitic intrusions (batholiths) are often surrounded by amphibolitic metamorphic rocks. Garnet (almandine), pyroxene, biotite, titanite, magnetite, epidote, chlorite, and quartz are also frequent constituents. Width of sample 16 cm. High grade dark-colored hornblende-bearing rock is hornblende gneiss. Metamorphic rocks are classified by their mineral composition, the source rock, also known as a protolith, and the context (pressure, temperature, hydrological features, etc.) Amphibolite is a very unfortunate name given to two very different things: a rock type, and a metamorphic facies. The temperature range of formation is usually 400…500 °C1. De Vore, George (2003). Some amphibolite deposits, such as the one at Gore Mountain in the Adirondacks of New York, contain significant amounts of garnet. Quartz, magnetite, and calcite can also be present in small amounts. The rare schistose varieties are transitional to related rocks like gneiss, granulite, eclogite and greenshist. It is also quarried and cut for use as a dimension stone. Arendal, Norway. Amphibolite is a common rock of the metamorphic facies with the same name. The amphiboles are usually members of the hornblende group. Amphibolite: This is a medium grade metamorphic rock. Some geologists call an igneous rock composed primarily of amphibole minerals an amphibolite or "hornblendite." Rock & Mineral Kits: Get a rock, mineral, or fossil kit to learn more about Earth materials. A contact between amphibolite (on the right) and tonalite pegmatite. If enough garnet is present and of proper quality, the amphibolite can be mined and the garnet recovered for use as an abrasive. But yet Thanks alOt ,it is worthy , It is really worthy ! Encyclopedia of Sediments & Sedimentary Rocks. Amphibolite is quarried and crushed for use as an aggregate in highway construction and as a ballast stone in railroad construction. Senja, Norway. 593-594. excellent , I realy enjoy from this site ,it is realy usefull for me thanks much, This is extremely helpful, especially because i am a high school student studying this particular rock. Amphibolite has a variety of uses in the construction industry. Most samples have a relatively simple composition: hornblende + plagioclase. As already noted, slate is formed from the low-grade metamorphism of shale, and has microscopic clay and mica crystals that have grown perpendicular to the stress. Amphibolite rarely hosts economic minerals, but the rock type is widely used as a construction material in road building (aggregate) and as a railroad ballast. However, not all amphibolites were formed within the pressure-temperature limits of the amphibolite facies and by no means are all rocks of this metamorphic facies amphibolites. Hullvann, Norway. So one should be careful when comparing amphibolitic rocks with the metamorphic facies that carries the same name. Main minerals in amphibolite are plagioclase (white) and hornblende. A contact between amphibolite (on the right) and tonalite pegmatite. Senja, Norway. of its formation. In: Encyclopedia of Sediments & Sedimentary Rocks (Ed. In order to make amphibolite out of basalt, we need heat and pressure to initiate chemical reactions and also need to add water because amphiboles, unlike pyroxenes, are hydrous minerals. : hornblende + plagioclase shiny because hornblende has a variety of igneous rock diorite and ultramafic rock hornblendite. and! Usually 400…500 °C1 the past to denote sedimentary and igneous protoliths, respectively an! 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