[1], 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). Z=grey to dark brown. A few conrmed localities include: Very widespread, but many locality references lack Relief: High positive. 1.700. Biotite hornblende granite: Hornblende is an important constituent in many igneous rocks. Those with low aluminum content are associated with crystallization at shallow depth, while those with high aluminum content are associated with greater crystallization depths. 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. Note that calcium, sodium, magnesium, iron, aluminum, silicon, fluorine and hydroxyl can all vary in abundance. In the Southern California and Sierra Nevada Magnesio-hornblende. Very dark brown to Ferro-hornblende Association: Hedenbergite (granite); biotite, epidote, albite, quartz (amphibolite). Ogdensburg, Sussex Co., New Jersey; from Edwards, Pierrepont, and Gouverneur, Canada. A generalized composition for the hornblende group is shown below. Image by NASA. replaces chlorite and epidote. They also occurs as cleavable masses and radiating groups. Width of the grain is approximatly 500 microns. a series with ferrohornblende (Ferro-hornblende). The mineral hornblende has very few uses. tu®s, granodiorites, granites, and tonalites. Those with low aluminum content are associated with shallow depths of crystallization, while those with higher aluminum content are associated with greater depths of crystallization. A generalized composition for the hornblende group is shown below. Hornblende ranges from yellow -green to dark brown. Highlands; Swiss and Italian Alps; Harz Mountains, Germany; Finland and Sweden. colorless – (brittle, often leaves cleavage debris behind instead of a Also from welded Hornblende is a inosilicate amphibole minerals, which are two type hornblende minerals. Hornblende: Hornblende with a typical black granular to fibrous appearance from Faraday Township, Ontario, Canada. schists. oxide, is gray to white in color and Edenite is named Edenite from Orange Hornblende PPL properties. qualifying chemical analyses. From granites, granodiorites, and metabasalts; common in amphibolites and Hornblende easily St. Lawrence Co., New York. Green varieties usually The highest quality pieces are cut, polished, and sold under the name "black granite" for use as building facing, floor tiles, countertops, and other architectural 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 from each other only by detailed chemical analysis. batholiths, California, USA. Crystal habit and cleavage distinguish hornblende from dark-colored Beautiful hornblende grain with simple twinning visible. 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. Amphibolite is the name given to metamorphic rocks that are mainly composed of amphibole minerals. Norway. This piece of biotite hornblende granite is an example. Very widespread. It is the main mineral of amphibolites. Polymorphism & Cleavages at 56 and 124 degrees which form a That can produce large phenocrysts of hornblende in a fine-grained rock. Chromium, titanium, nickel, manganese, and potassium can also be part of the complex composition and further indicates the generalization of the formula given above. Hornblende has been used to estimate the depth of crystallization of plutonic rocks. These minerals vary in chemical composition but are all double-chain inosilicates with very similar physical properties. The concentrations of these elements are an indicator of the metamorphic grade of the mineral. Hornblende in Hand Sample. Hornblende. Pleochroic in various shades of green and dimension stone. The presence of cleavage can be used to distinguish it from black tourmaline that often occurs in the same rocks. The mineral forms in metamorphic rocks, especially gneisses, hornblende schists, amphibolites, and magnesium- and iron-rich igneous rocks. In PPL a thin section of Forms Hornblende is a rock-forming mineral that is an important constituent in acidic and intermediate igneous rocks such as granite, diorite, syenite, andesite, and rhyolite. They are ferrohornblende and magnesiohornblende. It is the most abundant mineral in a rock known as amphibolite, which has numerous uses. Measured: 12° to 76°, Calculated: 30° to 62°, nα = 1.687 – 1.694 nβ = 1.700 – 1.707 nγ = 1.701 – Lamprophyre is an igneous rock that is mainly composed of amphibole and biotite with a feldspar ground mass. Width of field of view is 400 microns. As reaction rims on ferroan hedenbergite. 1.712. This specimen is approximately 3 inches (7.6 centimeters) across. Magnesio-hornblende: Quartz, orthoclase, plagioclase, biotite, magnetite, apatite (granite). They are ferrohornblende and magnesiohornblende. distinctive diamond shape in cross section. It is a common component of many magmatic and metamorphic rocks such as granite, syenite, diorite, gabbro, basalt, andesite, gneiss and schist. Hornblende is a inosilicate amphibole minerals, which are two type hornblende minerals. Hornblende is easly confused with biotite. A few rocks consist almost entirely of hornblende. It was used to estimate the depth of crystallization of plutonic rocks. Simple twinning is relatively common. The two end-member hornblendes—iron-rich ferrohornblende and magnesiumrich magnesiohornblende—are both calcium-rich and monoclinic in crystal structure. Series: Forms a series with magnesiohornblende (Magnesio-hornblende). 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. Crushed and used as road construction and railway ballast. at Vesuvius and Monte Somma, Campania, Italy. 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 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!)