Two cleavages intersect at 56 ° and 124 °. (2020). Norway. In PPL a thin section of Hornblende ranges from yellow -green to dark brown. brown. oxide, is gray to white in color and Edenite is named Edenite from Orange Very dark brown to Distiguishing factors are the lack of birds Fish Canyon Tuff . Specimens are green, dark green, or brownish green to black in color. Very widespread. 1.712. Rock-forming minerals of metamorphic rocks, in thin section (a work in progress) Atlas of Metamorphic Minerals. Length of larger sample: 1 mm. Quartz is the only other major constituent. Hornblende thin section photomicrographs are taken in plane-polarized light and cross-polarized light, and can easily be recognized under the microscope. Cleavage. Z=grey to dark brown. Its composition is variable and its general formula is (Ca,Mg,Al)Si8O22(OH)2. The two end-member hornblendes—iron-rich ferrohornblende and magnesiumrich magnesiohornblende—are both calcium-rich and monoclinic in crystal structure. In the granitic batholiths of the Scottish In PPL a thin section of varieties have X=greenish-yelow/brown, Y=yellowish to reddish brown and Series: Forms a series with magnesiohornblende (Magnesio-hornblende). PPL. 2 has been truncated normally to his long axis. Its color varies from dark-brown to dark-green, appearing black from a distance (as most mafic minerals). Brownish varieties have X=greenish-yelow/brown, Y=yellowish to reddish brown and Z=grey to dark brown. In the Southern California and Sierra Nevada Polymorphism & The content of amphibole and plagioclase together is mostly higher than 90%, and may be as low as 75%. Amphiboles; Double-chain Silicates. Highlands; Swiss and Italian Alps; Harz Mountains, Germany; Finland and Sweden. Note: We are using following thin section photos by having permission from their owners. Rock-forming minerals of metamorphic rocks, in thin section (a work in progress) ... 81 Hornblende Amphibole: blue-green hornblende, in garnet-grade metagabbro. They are ferrohornblende and magnesiohornblende. From Bancroft, Pakenham, and Eganville, Ontario, distinctive diamond shape in cross section. Crystals appear also light-green in plane-polarized thin sections and have vivid colors in crossed-polarized thin sections. Ferro-hornblende Association: Hedenbergite (granite); biotite, epidote, albite, quartz (amphibolite). Pleochroic in various shades of green and Cleavages at 56 and 124 degrees which form a Quartz is the only other major constituent. In the USA, from Franklin and Sterling Hill, Hornblende is easly confused with biotite. From Broken Hill, New South Wales, Australia. Other elements, such as chromium, titanium, and nickel, can also appear in the crystal structures of the group. Simple twinning is relatively common. Occurrence. An informal name for dark green to black amphiboles, mostly ferro-hornblende or magnesio-hornblende according to the current nomenclature. It is the main mineral of amphibolites. a series with ferrohornblende (Ferro-hornblende). On both photos hornblende pleichroism is evident as well as its cleavage with distinctive angles at 120 degrees. Brownish Shasta, California. It is the most abundant mineral in a rock known as amphibolite, which has numerous uses. Width of view: 8 mm. 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. Crystal System is Monoclinic; 2/m Crystal Habits include short stocky prismatic crystals as well as long thin crystal forms. as they are usually a component of basalt and related rocks. It is the principal mineral of amphibolites.Very dark brown to black hornblendes that contain titanium are ordinarily called basaltic hornblende, from the fact that they are usually a constituent of basalt and related rocks. In the book "Rock-forming minerals, volume 2b, double chain silicates" by Deer, Howie & Zussman (1997), the term "hornblende" is used as a group name for all aluminous amphiboles in the calcium amphibole subgroup of the Amphibole Supergroup. The mineral forms in metamorphic rocks, especially gneisses, hornblende schists, amphibolites, and magnesium- and iron-rich igneous rocks. The concentrations of these elements are an indicator of the metamorphic grade of the mineral. Notice the hole in its center. Magnesio-hornblende: Quartz, orthoclase, plagioclase, biotite, magnetite, apatite (granite). It was cut to be used as a dimension stone.