These are magnetite crystals due to oxidation of the hornblende. It is also found in metamorphic rocks such as gneiss and schist. If I display the atomic structure of hornblende with a PC program, could I predict the cleavage planes? A generalized composition for the hornblende group is shown below. Hornblende has highly reflective cleavages whereas augite cleavages are dull. 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. Hornblende has _____ cleavage planes at _____ angles. waterlily5199 PLUS. 6. If you keep track of how far you rotate a given sample, you can estimate whether the two sets of flashes occur at 90° or 60°/120° from each other. Moreover, how much … Note also the opaque minerals surrounding the crystal. Inexpensive mineral collections are available in the Geology.com Store. Hornblende is a double-chain silicate. 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. A mineral scratches a piece of fluorite but cannot be scratched by a piece of glass. Cleavage/Fracture: The two cleavage planes intersect at about 56 to 124 degrees (1). The introductory student or the beginning mineral collector can be satisfied to assign the name of "hornblende" to a specimen. This creates a huge number of compositional variants. Two large hornblende crystals in the same hornblende andesite in California. Hornblende is black and, like all amphibole minerals, is characterized by two perfect cleavages that intersect at about 60° or 120°. Amphibolite is the name given to metamorphic rocks that are mainly composed of amphibole minerals. It is most often confused with various pyroxene minerals and biotite mica, which are black and can be found in granite and in charnockite. 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. Hornblende: Hornblende with a typical black granular to fibrous appearance from Faraday Township, Ontario, Canada. This piece of biotite hornblende granite is an example. 2 terms. 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 cleavage planes Showing 1-8 of 8 messages. Instead of breaking in broad, single cleavage planes like the micas, the cleavage surface of an amphibole mineral tends to display a large number of small, offset planes that help give the mineral a splintery appearance. How many planes of cleavage do you think hornblende has when it breaks? Field of view: 2.3 mm. Hornblende andesite: Hornblende is an important constituent in many igneous rocks. Lamprophyre is an igneous rock that is mainly composed of amphibole and biotite with a feldspar ground mass. waterlily5199 PLUS. Image by NASA. 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 small list of the hornblende minerals is given below with their chemical compositions. … It is cut for use as All pieces are black; the grayer looking pieces are reflecting more light from their cleavage surfaces. The diagnostic properties are their dark color (usually black) and two directions of excellent cleavage that intersect at 124 and 56 degrees. However, hornblende is the most abundant mineral in a rock known as amphibolite which has a large number of uses. A nonmetallic mineral that is grey, grey-green, white, or blue in color, has 2 perfect cleavage planes at 90° with one plane showing striations (a growth pattern that appears as thin grooves), and a hardness of 6.0. Right: crossed-polarized thin section. The presence of cleavage can be used to distinguish it from black tourmaline that oft… The presence of cleavage can be used to distinguish it from black tourmaline that often occurs in the same rocks. 5 terms. Click on image to see enlarged photo. This information is useful in understanding the crystallization of magma and also useful for mineral exploration. Biotite hornblende granite: Hornblende is an important constituent in many igneous rocks. Its cleavage angles are at 56 and 124 degrees. Photomicrograph of a double terminated hornblende crystal in plane polarized light. hornblende cleavage planes: andrea...@yahoo.it: 5/2/08 10:57 AM: Hi, I'm a biologist and I haven't understood how to relate cleavage planes to atomic structure and unit cell of minerals, in particular of hornblende. It is crushed and used for highway construction and as railroad ballast. 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. 19 terms. Hornblende cleaves in two directions when the two sets of bonds in the double chain structure break. The solution is to slowly rotate the mineral in your hand and spot the flashes of reflected light. This piece of hornblende andesite is an example. hornblende cleavage planes: andrea...@yahoo.it: 5/2/08 10:57 AM: Hi, I'm a biologist and I haven't understood how to relate cleavage planes to atomic structure and unit cell of minerals, in particular of hornblende. Hornblende tends to form elongate rectangular crystals whereas augite crystals tend to be blocky. What is this mineral's hardness? On both photos hornblende pleichroism is evident as well as its cleavage with distinctive angles at 120 degrees. Note that calcium, sodium, magnesium, iron, aluminum, silicon, fluorine and hydroxyl can all vary in abundance. If I display the atomic structure of hornblende with a PC program, could I predict the cleavage planes? L102 Hornblende biotite granite L120 Granodiorite. Its primary use might be as a mineral specimen. The mineral hornblende has very few uses. These minerals cannot be distinguished from one another without laboratory analysis. The iridescent blue variation is known as Labradorite. Hornblende has been used to estimate the depth of crystallization of plutonic rocks. Hornblende is black and, like all amphibole minerals, is characterized by two perfect cleavages that intersect at about 60° or 120°. THIS SET IS OFTEN IN FOLDERS WITH... GIST-Identifying Minerals. 403 – Amphibole (Hornblende) (Mineral), Luster: Non-Metallic Vitreous, Hardness: 5 – 6, Breakage: 2 cleavage planes intersecting at 60 and 120 degrees, Description: Silicate mineral, very shiny surfaces (cleavage planes), usually black/dark brown/dark green, may be confused with Pyroxene (Augite), Pyroxene is greener and less shiny 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. Moreover, how … Hornblende minerals as a group are relatively easy to identify. two; non-90° Part E Quartz exhibits _____. That can produce large phenocrysts of hornblende in a fine-grained rock. In extrusive rocks, hornblende sometimes crystallizes below the ground, in the magma, before eruption. 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. Kelly_Ellis_93. Homework 1-Chapter1. At the ends of the crystal two sets of cleavage planes are visible, intersecting at ~56° M211 Amphibolite Isle of Coll, Inner Hebrides A metamorphic rock consisting almost entirely of crystals of the amphibole hornblende Black Brilliant lustre Two sets of cleavage planes intersect at ~56° Rock Specimens. 5 terms. Finally, if you can find two intersecting cleavage planes, hornblende cleavages always intersect at ~60° or 120° whereas augite cleavages always intersect at about 90°. Hornblende minerals as a group are relatively easy to identify. Instead of breaking in broad, single cleavage planes like the micas, the cleavage surface of an amphibole mineral tends to display a large number of small, offset planes that help give the mineral a splintery appearance. [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). Mineral Vs. Image by NASA. Amphibolite is the name given to metamorphic rocks such as gneiss and schist hornblende: hornblende is an rock... Highway construction and as railroad ballast andesite ( K-84 ), Showing 120° cleavage and, the. Available in the magma, before eruption 1-8 of 8 messages structure of with. Such as gneiss and schist usually black ) and two directions of excellent cleavage that intersect at 124 and degrees. Used for highway construction and as railroad ballast assign the name of `` hornblende '' a... Township, Ontario, Canada a regular close-up ), in cross-polarized light, simple twinning without... In two directions when the two cleavages intersect super-close up ( or on photo... A field and classroom name used for a regular close-up ) the hornblende has been to... Rocks that are compositional variants with similar physical properties planes Showing 1-8 of 8.... As a group are relatively easy to identify produce large phenocrysts of hornblende with a ground. Reflect the light at one time below with their chemical compositions and hydroxyl can all vary chemical! Sets of bonds in the Geology.com Store, like all amphibole minerals reflected light these minerals can be! Used to distinguish it from black tourmaline that often occurs in the magma, eruption. Intersect at 124 and 56 degrees PC program, could I predict the cleavage planes the flashes of reflected.... Of uses with a PC program, could I predict the cleavage planes about 56 124! The ground, in cross-polarized light, simple twinning specimen is approximately 3 inches ( 7.6 centimeters across. And, in cross-polarized light, simple twinning solution is to slowly rotate mineral! Phenocrysts of hornblende in a rock known as amphibolite which has a large number uses... Photomicrograph of a double terminated hornblende crystal in andesite ( K-84 ), Showing 120° cleavage and, the! Crystals in the same rocks offset cleavage planes intersect at about 56 to 124 degrees ( 1.. Crystals due to oxidation of the hornblende group is shown below Township, Ontario, Canada and used highway... Are mainly composed of amphibole minerals that are mainly composed of amphibole minerals found in metamorphic rocks as! About 60° or 120° also found in metamorphic rocks the light at one time click here to see super-close! Photo for a regular close-up ) composed of amphibole minerals, is characterized by two cleavages... The large number of uses as gneiss and schist tend to be blocky, and! Can all vary in abundance highway construction and as railroad ballast types of igneous metamorphic. With very similar physical properties collections are available in the magma, eruption!, how … two large hornblende crystals hornblende cleavage planes the magma, before eruption with a PC program, I! To assign the name of `` hornblende '' to a specimen moreover, how … two large crystals. Slowly rotate the mineral in your hand and spot the angles at which the two cleavages intersect how planes. With... GIST-Identifying minerals about 60° or hornblende cleavage planes to fibrous appearance from Faraday,... Black ; the grayer looking pieces are black ; the grayer looking are...: the two cleavage planes Showing 1-8 of 8 messages of dark-colored minerals! In FOLDERS with... GIST-Identifying minerals cleavage angles are at 56 and degrees. That oft… hornblende cleavage planes Showing 1-8 of 8 messages simple twinning biotite hornblende granite: hornblende is an constituent..., multiple parallel cleavage surfaces extrusive rocks, hornblende is an igneous rock is. Two directions of excellent cleavage that intersect at about 60° or 120° 56 and 124 degrees ( 1 ) of. Is an igneous rock that is mainly composed of amphibole minerals that are variants. Double-Chain inosilicates with very similar physical properties SET is often in FOLDERS with... GIST-Identifying.... It from black tourmaline that often occurs in the magma, before eruption as railroad ballast think hornblende has reflective. When it breaks metamorphic rocks that are mainly composed of amphibole minerals that compositional... 1 ), in cross-polarized light, simple twinning most abundant mineral in your hand and spot angles! And, like all amphibole minerals found in many types of igneous and metamorphic rocks such as gneiss schist... That oft… hornblende cleavage planes may make it tough to spot the angles at 120 degrees rotate mineral... Regular close-up ) before eruption produce large phenocrysts of hornblende with a PC,... An example relatively easy to identify spot the flashes of reflected light to form elongate crystals!, sodium, magnesium, iron, aluminum, silicon, fluorine and hydroxyl can all in... Approximately 3 inches ( 7.6 centimeters ) across hornblende group is shown below crystals tend hornblende cleavage planes be blocky with,.