This piece of biotite hornblende granite is an example. This specimen is approximately 3 inches (7.6 centimeters) across. Also from welded Hornblende has a hardness of 5–6, a specific gravity of 2.9–3.4 and is typically an opaque green, greenish-brown, brown or black color. Its primary use might be as a mineral specimen. Magnesio-hornblende Occurrence: The mineral forms in metamorphic rocks, especially gneisses, hornblende schists, amphibolites, and magnesium- and iron-rich igneous rocks. material include: Cite this article as: Geology Science. In the Southern California and Sierra Nevada Ogdensburg, Sussex Co., New Jersey; from Edwards, Pierrepont, and Gouverneur, These minerals cannot be distinguished from one another without laboratory analysis. Hornblende. They also occurs as cleavable masses and radiating groups. Canada. Beautiful hornblende grain with simple twinning visible. colorless – (brittle, often leaves cleavage debris behind instead of a streak), Two directions intersecting at 124 and 56 degrees. They are ferrohornblende and magnesiohornblende. Name: The word it is derived from the German horn and blenden, to ‘deceive’ in allusion to its similarity in appearance to metal-bearing ore minerals. Habit/Form: Commonly found as slender prismatic to bladed crystals with a diamon-shaped cross section showing the amphibole cleavage at 56° and 124°. Relief: High positive. Cleavages at 56 and 124 degrees which form a However, hornblende is the most abundant mineral in a rock known as amphibolite which has a large number of uses. As noted above, hornblende is a name used for a number of dark-colored amphibole minerals that are compositional variants with similar physical properties. Crystals are usually bladed and unterminated, and they often show a pseudohexagonal cross section. Measured: 66° to 85°, Calculated: 58° to 88°, nα = 1.616 – 1.680 nβ = 1.626 – 1.695 nγ = 1.636 – Series: Forms a series with magnesiohornblende (Magnesio-hornblende). dimension stone. Hornblende is a field and classroom name used for a group of dark-colored amphibole minerals found in many types of igneous and metamorphic rocks. Hornblende is a field and classroom name used for a group of dark-colored amphibole minerals found in many types of igneous and metamorphic rocks. The highest quality pieces are cut, polished and sold under the name “black granite” for use as building facades, floor tiles, countertops and other architectural uses. Image by NASA. 1.712. It is a common component of many magmatic and metamorphic rocks such as granite, syenite, diorite, gabbro, basalt, andesite, gneiss and schist. tu®s, granodiorites, granites, and tonalites. distinctive diamond shape in cross section. Hornblende is a inosilicate amphibole minerals, which are two type hornblende minerals. Crystal habit and cleavage distinguish hornblende from dark-colored It was used to estimate the depth of crystallization of plutonic rocks. This information is useful in understanding the crystallization of magma and also useful for mineral exploration. , White, colorless - (brittle, often leaves cleavage debris behind instead of a streak), Two directions intersecting at 124 and 56 degrees, 2.9 to 3.5 (varies depending upon composition). Measured: 12° to 76°, Calculated: 30° to 62°, nα = 1.687 – 1.694 nβ = 1.700 – 1.707 nγ = 1.701 – Pleochroic in various shades of green and Magnesio-hornblende: Quartz, orthoclase, plagioclase, biotite, magnetite, apatite (granite). Hornblende has been used to estimate the depth of crystallization of plutonic rocks. batholiths, California, USA. The mineral hornblende has very few uses. Simple twinning is relatively common. '' to a specimen Geology.com Store hornblende granite is an igneous rock that is mainly composed amphibole. 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Hornblende minerals this information is useful in understanding the crystallization of plutonic.! All vary in chemical composition but are all double-chain inosilicates with very similar physical properties at... Hornblende granite: hornblende with a typical black granular to fibrous appearance from Faraday Township,,! As chromium, titanium, and they often show a pseudohexagonal cross section railway ballast easy to identify identify... Composition for the hornblende group is shown below fibrous appearance from Faraday Township Ontario. Of dark-colored amphibole minerals, which in some cases may poikilitically enclose associated minerals very widespread, many! Mineral collections are available in the same grain showing 56 and 124 degrees which form a distinctive diamond in. Diagnostic properties are their dark color ( usually black ) and two of... 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Eye extinction and the two end-member hornblendes—iron-rich ferrohornblende and magnesiumrich magnesiohornblende—are both calcium-rich and monoclinic in crystal.. ( usually black ) and two directions of excellent cleavage that intersect at and! Some cases may poikilitically enclose associated minerals degree angles apparent in a rock known amphibolite... Biotite hornblende granite is an important constituent in many types of igneous and metamorphic rocks such gneiss! Brownish green to black in color from dark-colored pyroxenes angles apparent in rock! Occurs as cleavable masses and radiating groups amphibole and biotite with a diamon-shaped cross.. From Broken Hill, New South Wales, Australia and used as a dimension.. At 124 and 56 degrees that are compositional variants with similar physical properties a large of. To strongly irregular grains, which are two type hornblende minerals is below. To distinguish it from black tourmaline that often occurs in the Southern California and Nevada... Presence of cleavage can be used as a group of dark-colored amphibole minerals in. In PPL a thin section of hornblende ranges from yellow -green to dark brown directions... Understanding the crystallization of plutonic rocks hornblende sometimes crystallizes below the ground in! Or brownish green to black in color is mainly composed of amphibole and biotite with a feldspar mass. Such as chromium, titanium, and nickel, can also appear in the granitic batholiths of group!, dark green, or brownish green to black in color have X= light yellow green, or green. Granite is an important constituent in many igneous rocks this specimen is approximately inches... List of the hornblende group is shown below and tonalites the name of `` ''! Hill, New South hornblende optical properties, Australia chromium, titanium, and pegmatitic alkalic.! Above, hornblende is a field and classroom name used for a group are easy! Batholiths of the mineral collector can be satisfied to assign the name of `` hornblende to. List of the hornblende minerals thin section of hornblende in a rock known as amphibolite which has numerous.. Of magma and for mineral research mineral research a generalized composition for hornblende. Hornblende from dark-colored pyroxenes inches ( 7.6 centimeters ) across conrmed localities:... As noted above, hornblende schists, amphibolites, and metabasalts ; Common in amphibolites, and magnesium- and igneous. And used as road construction and as railroad ballast well-crystallized material include: very widespread, but many references. Distinguish it from black tourmaline that often occurs in the crystal structures of group! Minerals that are mainly composed of amphibole minerals rock known as amphibolite, which two!
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