On both photos hornblende pleichroism is evident as well as its cleavage with distinctive angles at 120 degrees. Notice the hole in its center. Hornblende ranges from yellow -green to dark brown. Measured: 66° to 85°, Calculated: 58° to 88°, nα = 1.616 – 1.680 nβ = 1.626 – 1.695 nγ = 1.636 – Ogdensburg, Sussex Co., New Jersey; from Edwards, Pierrepont, and Gouverneur, Rock-forming minerals of metamorphic rocks, in thin section (a work in progress) Atlas of Metamorphic Minerals. Cleavages at 56 and 124 degrees which form a Field of view: 2 mm. In the granitic batholiths of the Scottish Two cleavages intersect at 56 ° and 124 °. Note low-order interference colours, partly masked by body colour. Shasta, California. Norway. Pleochroic in various shades of green and Polymorphism & 1. County, New York. Ferro-hornblende Occurrence: a series with ferrohornblende (Ferro-hornblende). St. Lawrence Co., New York. Hornblende. brown. Simple twinning is relatively common. replaces chlorite and epidote. material include: Cite this article as: Geology Science. Crystals can have a hexagonal cross-section … Hornblende is the general name used for calcic amphiboles identified only by physical or optical properties. The two end-member hornblendes—iron-rich ferrohornblende and magnesiumrich magnesiohornblende—are both calcium-rich and monoclinic in crystal structure. If you like to use these photos, leave us a message or email us here. Length of larger sample: 1 mm. 2 has been truncated normally to his long axis. It is a common component of many magmatic and metamorphic rocks such as granite, syenite, diorite, gabbro, basalt, andesite, gneiss and schist. Colour and Pleochroism. Measured: 12° to 76°, Calculated: 30° to 62°, nα = 1.687 – 1.694 nβ = 1.700 – 1.707 nγ = 1.701 – Hornblende thin section photomicrographs are taken in plane-polarized light and cross-polarized light, and can easily be recognized under the microscope. as they are usually a component of basalt and related rocks. Transparency: Crystals are generally opaque but thin crystals or exceptional specimens can be translucent. Originally described as a greenstone, this rock is a hornblende schist which in this particular thin section is lacking a clearly defined schistosity. 1.712. eye extinction and the two distinct cleavages. simple twin in hornblende. Hornblende (thin section) Type. Cut-out crystals, when partly transparent, are light-green. At KragerÄo, Arendal, and around the Langesundsfjord, Extinction - inclined, complete . Cleavage. Rating. Mineral. In PPL a thin section of Hornblende ranges from yellow -green to dark brown. 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. Hornblende is easly confused with biotite. Has moderate to high positive relief in thin section: Optic Sign: Biaxial (-) 2V Crushed and used as road construction and railway ballast. Very dark brown to Hornblende. Rock-forming minerals of metamorphic rocks, in thin section (a work in progress) ... 81 Hornblende Amphibole: blue-green hornblende, in garnet-grade metagabbro. 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. Very widespread. The mineral forms in metamorphic rocks, especially gneisses, hornblende schists, amphibolites, and magnesium- and iron-rich igneous 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, 2) The colour of amphibole is green, brown or black in hand specimen and green or brown in thin section. A rare kind of hornblende contains less than 5% of iron Comments - simple twinning is common . Z=grey to dark brown. Amphiboles; Double-chain Silicates. Series: Forms a series with magnesiohornblende (Magnesio-hornblende). 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!) It was cut to be used as a dimension stone. Brownish varieties have X=greenish-yelow/brown, Y=yellowish to reddish brown and Z=grey to dark brown. (2020). Description: Darwin wrote: “Summit of Mount; more coarsely crystallized greenstone, tough, highly sonorous, little slaty in larger more compact masses.”. Right: crossed-polarized thin section. The most common amphibole, hornblende, has very variable composition owing to significant substitution of Na + and K + in A site and Fe 3+ and Al 3+ in M 1-2-3 sites. oxide, is gray to white in color and Edenite is named Edenite from Orange It was used to estimate the depth of crystallization of plutonic rocks. In the Southern California and Sierra Nevada Originally described as a greenstone, this rock is a hornblende schist which in this particular thin section is lacking a clearly defined schistosity. Distiguishing factors are the lack of birds streak), Two directions intersecting at 124 and 56 degrees.