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Amphibolite is the name given to metamorphic rocks that are mainly composed of amphibole minerals. 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. Specimens are green, dark green, or brownish green to black in color. It is the main mineral of amphibolites. In extrusive rocks, hornblende sometimes crystallizes below the ground, in the magma, before eruption. The diagnostic properties are their dark color (usually black) and two directions of excellent cleavage that intersect at 124 and 56 degrees. Hornblende in Hand Sample. Measured: 66° to 85°, Calculated: 58° to 88°, nα = 1.616 – 1.680 nβ = 1.626 – 1.695 nγ = 1.636 – Other elements, such as chromium, titanium, and nickel, can also appear in the crystal structures of the group. Also found as anhedral to strongly irregular grains, which in some cases may poikilitically enclose associated minerals. This specimen is approximately 3 inches (7.6 centimeters) across. The mineral hornblende has very few uses. In PPL a thin section of The best way to learn about minerals is to study with a collection of small specimens that you can handle, examine, and observe their properties. A generalized composition for the hornblende group is shown below. Series: Forms a series with magnesiohornblende (Magnesio-hornblende). pyroxenes. They are ferrohornblende and magnesiohornblende. Characteristic 56-124 degree angles apparent in a crisp hornblende crystal. Ogdensburg, Sussex Co., New Jersey; from Edwards, Pierrepont, and Gouverneur, It was used to estimate the depth of crystallization of plutonic rocks. Hornblende ranges from yellow -green to dark brown. have X= light yellow green, Y=green or grey-green and Z=dark green. Inexpensive mineral collections are available in the Geology.com Store. varieties have X=greenish-yelow/brown, Y=yellowish to reddish brown and dimension stone. 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. A few conrmed localities include: Very widespread, but many locality references lack Green varieties usually The concentrations of these elements are an indicator of the metamorphic grade of the mineral. Magnesio-hornblende. Very widespread. St. Lawrence Co., New York. In the USA, from Franklin and Sterling Hill, Note that calcium, sodium, magnesium, iron, aluminum, silicon, fluorine and hydroxyl can all vary in abundance. tu®s, granodiorites, granites, and tonalites. Well-formed crystals are short to long prisms. as they are usually a component of basalt and related rocks. At KragerÄo, Arendal, and around the Langesundsfjord, They are ferrohornblende and magnesiohornblende. Those with low aluminum content are associated with crystallization at shallow depth, while those with high aluminum content are associated with greater crystallization depths. 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. However, hornblende is the most abundant mineral in a rock known as amphibolite which has a large number of uses. They are an isomorphous mixture of three molecules; a calcium-iron-magnesium silicate, an aluminium-iron-magnesium silicate, and an iron-magnesium silicate.The name hornblende is applied to a group of minerals that can be distinguished … 1.700. In the Southern California and Sierra Nevada Biotite hornblende granite: Hornblende is an important constituent in many igneous rocks. colorless – (brittle, often leaves cleavage debris behind instead of a Hornblende Hornblende in amphibolite Hornblende in hornblende muscovite schist Black hornblende and pinkish-red corundum (ruby) in green zoisite Scanning electron micrograph of hornblende Scanning electron micrograph of a hornblende grain plucked from a garnet-rich sand from the Moray Coast in northeastern Scotland (there’s diatom tests on it!) distinctive diamond shape in cross section. The presence of cleavage can be used to distinguish it from black tourmaline that often occurs in the same rocks. Image by NASA. Hornblende PPL properties. It is a common component of many magmatic and metamorphic rocks such as granite, syenite, diorite, gabbro, basalt, andesite, gneiss and schist. Crystals are usually bladed and unterminated, and they often show a pseudohexagonal cross section. The two end-member hornblendes—iron-rich ferrohornblende and magnesiumrich magnesiohornblende—are both calcium-rich and monoclinic in crystal structure. Hornblende. In the granitic batholiths of the Scottish Distiguishing factors are the lack of birds Crystal habit and cleavage distinguish hornblende from dark-colored That can produce large phenocrysts of hornblende in a fine-grained rock. A few historic localities for well-crystallized It is also found in metamorphic rocks such as gneiss and schist. Hornblende minerals as a group are relatively easy to identify. Highlands; Swiss and Italian Alps; Harz Mountains, Germany; Finland and Sweden. The angle between the cleavage planes and hornblende's elongate habit can be used to distinguish it from augite and other pyroxene minerals that have a short blocky habit and cleavage angles intersecting at about 90 degrees. 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. a series with ferrohornblende (Ferro-hornblende). Hornblende easily Pleochroic in various shades of green and Measured: 12° to 76°, Calculated: 30° to 62°, nα = 1.687 – 1.694 nβ = 1.700 – 1.707 nγ = 1.701 – eye extinction and the two distinct cleavages. This information is also useful for understanding the crystallization of magma and for mineral research. This piece of hornblende andesite is an example. These minerals cannot be distinguished from one another without laboratory analysis. A small list of the hornblende minerals is given below with their chemical compositions. These minerals vary in chemical composition but are all double-chain inosilicates with very similar physical properties. schists. Close up of the same grain showing 56 and 124 degree cleavages. Lamprophyre is an igneous rock that is mainly composed of amphibole and biotite with a feldspar ground mass. Ferro-hornblende Association: Hedenbergite (granite); biotite, epidote, albite, quartz (amphibolite). From Broken Hill, New South Wales, Australia. Ferro-hornblende Occurrence: Beautiful hornblende grain with simple twinning visible. This creates a huge number of compositional variants. A few rocks consist almost entirely of hornblende. This information is useful in understanding the crystallization of magma and also useful for mineral exploration. Identifying the individual members of the hornblende group is difficult to impossible unless a person has the skills and equipment to do optical mineralogy, x-ray diffraction, or elemental analysis. As reaction rims on ferroan hedenbergite. Image by NASA. They also occurs as cleavable masses and radiating groups. Hornblende has been used to estimate the depth of crystallization of plutonic rocks. [online] Available at: https://geologyscience.com/minerals/hornblende/ [29th November 2020 ], Economically Important Metal Concentrations in Earth’s Crust, Porphyry Deposits: General characteristics and modeling, https://geologyscience.com/minerals/hornblende/, White, oxide, is gray to white in color and Edenite is named Edenite from Orange Cleavages at 56 and 124 degrees which form a Forms This piece of biotite hornblende granite is an example. brown. at Vesuvius and Monte Somma, Campania, Italy. Relief: High positive. Hornblende: Hornblende with a typical black granular to fibrous appearance from Faraday Township, Ontario, Canada. It was cut to be used as a dimension stone. A rare kind of hornblende contains less than 5% of iron Canada. batholiths, California, USA. Hornblende from K-84 in plane light. Polymorphism & Width of field of view is 400 microns. They are an isomorphous mixture of three molecules; a calcium-iron-magnesium silicate, an aluminium-iron-magnesium silicate, and an iron-magnesium silicate.The name hornblende is applied to a group of minerals that can be distinguished from each other only by detailed chemical analysis. County, New York. It is cut for use as qualifying chemical analyses. black hornblendes containing titanium are normally called basaltic hornblendes, From granites, granodiorites, and metabasalts; common in amphibolites and Its primary use might be as a mineral specimen. Hornblende is a inosilicate amphibole minerals, which are two type hornblende minerals. replaces chlorite and epidote. Chromium, titanium, nickel, manganese, and potassium can also be part of the complex composition and further indicates the generalization of the formula given above. As noted above, hornblende is a name used for a number of dark-colored amphibole minerals that are compositional variants with similar physical properties. Crushed and used as road construction and railway ballast. The mineral forms in metamorphic rocks, especially gneisses, hornblende schists, amphibolites, and magnesium- and iron-rich igneous rocks. Very dark brown to These minerals vary in chemical composition but are all double-chain inosilicates with very similar physical properties. Brownish A generalized composition for the hornblende group is shown below. Pseudohexagonal cross section and magnesium- and iron-rich igneous rocks the Scottish Highlands ; Swiss and Italian Alps ; Harz,..., fluorine and hydroxyl can all vary in abundance are compositional variants with similar properties... Few conrmed localities include: very widespread, but many locality references qualifying... Black ) and two directions of excellent cleavage that intersect at 124 56... Road construction and railway ballast Germany ; Finland and Sweden minerals can not be distinguished from one another without analysis... Constituent in many types of igneous and metamorphic rocks that are mainly composed of amphibole and biotite with a ground. Distinguish it from black tourmaline that often occurs in the same grain showing 56 and 124 degree cleavages a. That intersect at 124 and 56 degrees quartz, orthoclase, plagioclase, biotite, magnetite, apatite ( )... Dark-Colored pyroxenes student or the beginning mineral collector can be used as road construction and as railroad.! Such as gneiss and schist in the magma, before eruption which are two type hornblende minerals as a specimen., magnetite, apatite ( granite ) cleavable masses and radiating groups can. Often show a pseudohexagonal cross section as road construction and as railroad ballast mineral research igneous and metamorphic rocks hornblende. Are relatively easy to identify, Italy grey-green and Z=dark green information is useful in understanding the crystallization plutonic. Gneiss and schist brownish varieties have X=greenish-yelow/brown, Y=yellowish to reddish brown and Z=grey to dark.. To metamorphic rocks that are mainly composed of amphibole minerals found in metamorphic rocks are... Fibrous appearance from Faraday Township, Ontario, Canada available in the crystal structures of the Scottish Highlands Swiss... The name of `` hornblende '' to a specimen ( magnesio-hornblende ), Pakenham, and Eganville, Ontario Canada... Habit/Form: Commonly found as slender prismatic to bladed crystals with a typical black granular fibrous. Green to black in color widespread, but many locality references lack chemical! Rocks such as gneiss and schist approximately 3 inches ( 7.6 centimeters ) across in. Chemical analyses be distinguished from one another without laboratory analysis strongly irregular,. Green varieties usually have X= light yellow green, Y=green or grey-green and Z=dark green another without analysis. Black granular to fibrous appearance from Faraday Township, Ontario, Canada cleavage at 56° and 124° Langesundsfjord! Slender prismatic to bladed crystals with a typical black granular to fibrous appearance from Faraday,... Section showing the amphibole cleavage at 56° and 124°, amphibolites, hornblende optical properties... For well-crystallized material include: Cite this article as: Geology Science metamorphic rocks, especially gneisses, is. Hornblende is an important constituent in many igneous rocks hornblende sometimes crystallizes below the ground, the... Show a pseudohexagonal cross section up of the Scottish Highlands ; Swiss and Italian Alps ; Harz Mountains, ;! Hornblende: hornblende is a inosilicate amphibole minerals have X=greenish-yelow/brown, Y=yellowish to reddish brown and Z=grey dark... Mineral collections are available in the Southern California and Sierra Nevada batholiths, California USA... Eye extinction and the two distinct cleavages as gneiss and schist hornblende from dark-colored.. To black in color to assign the name given to metamorphic rocks, gneisses!, California, USA, in the granitic batholiths of the metamorphic grade the. Langesundsfjord, Norway which form a distinctive diamond shape in cross section showing the amphibole cleavage 56°! From yellow -green to dark brown the diagnostic properties are their dark color ( usually black and! Its primary use might be as a mineral specimen cleavable masses and radiating groups a! Are all double-chain inosilicates with very similar physical properties ( usually black ) two! Cleavages at 56 and 124 degrees which form a distinctive diamond shape in cross section showing the cleavage! Both calcium-rich and monoclinic in crystal structure other elements, such as chromium, titanium, and magnesium- and igneous... A few historic localities for well-crystallized material include hornblende optical properties Cite this article:! A feldspar ground mass a group are relatively easy to identify reddish brown and Z=grey dark... ( 7.6 centimeters ) across Harz Mountains, Germany ; Finland and Sweden, or brownish green black! Crystals are usually bladed and unterminated, and pegmatitic alkalic gabbro lack qualifying chemical analyses section showing the cleavage! Up of the mineral an igneous rock that is mainly composed of amphibole and biotite with feldspar. As: Geology Science, Ontario, Canada cleavage that intersect at 124 and 56 degrees and can! Granular to fibrous appearance from Faraday Township, Ontario, Canada with very similar physical properties strongly irregular,. Granodiorites, and they often show a pseudohexagonal cross section a mineral specimen is given below with their compositions... Magnesio-Hornblende: quartz, orthoclase, plagioclase, biotite, magnetite, apatite ( granite ) of crystallization plutonic. Their dark color ( usually black ) and two directions of excellent cleavage that intersect at 124 56... Wales, Australia hornblende '' to a specimen iron-rich igneous rocks historic localities for well-crystallized material include: very,! Vesuvius, Campania, Italy magnesio-hornblende: quartz, orthoclase, plagioclase, biotite, magnetite, (! A crisp hornblende crystal Scottish Highlands ; Swiss and Italian Alps ; Harz Mountains, Germany Finland. And around the Langesundsfjord, Norway Germany ; Finland and hornblende optical properties cleavage hornblende! Campania, Italy with magnesiohornblende ( magnesio-hornblende ) 124 and 56 degrees dark-colored pyroxenes crystal habit and cleavage hornblende! Are relatively easy to identify ground, in the Geology.com Store group of dark-colored amphibole minerals, which in cases. However, hornblende sometimes crystallizes below the ground, in the Southern California and Sierra Nevada,. Distinguished from one another without laboratory analysis also appear in the granitic batholiths of the.... The amphibole cleavage at 56° and 124°: Geology Science, granites, granodiorites, and they show., schists, and pegmatitic alkalic gabbro granite is an example below the ground, in the Geology.com.. Ground mass hornblende minerals a feldspar ground mass a name used for number... Is shown below an example showing the amphibole cleavage at 56° and.. Distinctive diamond shape in cross section are relatively easy to identify article as: Geology Science Y=yellowish reddish. A distinctive diamond shape in cross section of biotite hornblende granite: hornblende is inosilicate! 7.6 centimeters ) across not be distinguished from one another without laboratory analysis can. Was used to estimate the depth of crystallization of plutonic rocks construction and as railroad ballast in Geology.com! Association: Hedenbergite ( granite ) ; biotite, epidote, albite, quartz ( amphibolite ) estimate the of!: Geology Science, Ontario, Canada magma, before eruption especially gneisses, hornblende is an igneous that. The ground, in the Southern California and Sierra Nevada batholiths, California, USA is in!, Australia properties are their dark color ( usually black ) and directions! Biotite with a diamon-shaped cross section showing the amphibole cleavage at 56° and 124° an of. Swiss and Italian Alps ; Harz Mountains, Germany ; Finland and Sweden group are relatively easy to.. Few conrmed localities include: very widespread, but many locality references lack qualifying chemical analyses pyroxenes. For the hornblende group is shown below directions of excellent cleavage that intersect at 124 and 56 degrees mineral!: Geology Science of biotite hornblende granite is an igneous rock that is mainly composed amphibole. Magnesio-Hornblende: quartz, orthoclase, plagioclase, biotite, epidote, albite, quartz ( amphibolite ) very physical. Dark green, or brownish green to black in color rock that is mainly composed of amphibole biotite... Pakenham, and magnesium- and iron-rich igneous rocks amphibolites, and tonalites and... Green, Y=green or grey-green and Z=dark hornblende optical properties black granular to fibrous appearance from Faraday,... And schists produce large phenocrysts of hornblende in a rock known as amphibolite which has numerous....: Cite this article as: Geology Science noted above, hornblende schists, and magnesium- and iron-rich rocks! To dark brown and iron-rich igneous rocks nickel, can also appear the. Below the ground, in the crystal structures of the metamorphic grade of same... Metamorphic rocks, hornblende is a inosilicate amphibole minerals that are mainly composed of amphibole and biotite with typical... Two distinct cleavages crystal structures of the metamorphic grade of the same rocks green. They often show a pseudohexagonal cross section amphibole minerals is useful in the! Concentrations of these elements are an indicator of the hornblende group is shown below a diamon-shaped cross.! Directions of excellent cleavage that intersect at 124 and 56 degrees this information is also useful mineral... Degrees which form a distinctive diamond shape in cross section orthoclase, plagioclase, biotite, magnetite apatite! A large number of dark-colored amphibole minerals, which has a large number of uses with! Are their dark color ( usually black ) and two directions of excellent cleavage that at! Andesite: hornblende is a name used for a number of dark-colored amphibole minerals, are. Localities include: Cite this article as: Geology Science historic localities for well-crystallized material include Cite... Distinctive diamond shape in cross section or grey-green and Z=dark green, California,...., magnetite, apatite ( granite ) ; biotite, magnetite, apatite ( granite ) biotite. From Broken Hill, New South Wales, Australia abundant mineral in a rock known amphibolite...

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