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20-596: Around Mount Job, rhyodacite contains hornblende , biotite and quartz . On the east side of the Affliction Glacier, rhyodacite of the Job Assemblage overlies porphyritic andesite of the older Pylon Assemblage . The more recently formed Capricorn Assemblage overlies the Job Assemblage at the head of Affiction Glacier and Capricorn Glacier. This article about a location on the Coast of British Columbia , Canada

40-449: A positively charged brucite layer. Chlorite is considered a clay mineral . It is a nonswelling clay mineral, since water is not adsorbed in the interlayer spaces, and it has a relatively low cation exchange capacity . Chlorite is a common mineral, found in metamorphic, igneous, and sedimentary rocks. It is an important rock-forming mineral in low- to medium-grade metamorphic rock formed by metamorphism of mafic or pelitic rock. It

60-463: A wide variety of compositions, in which magnesium, iron, aluminium, and silicon substitute for each other in the crystal structure. A complete solid solution series exists between the two most common end members, magnesium-rich clinochlore and iron-rich chamosite . In addition, manganese, zinc, lithium, and calcium species are known. The great range in composition results in considerable variation in physical, optical, and X-ray properties. Similarly,

80-424: Is (Ca,Na) 2−3 (Mg,Fe,Al) 5 (Al,Si) 8 O 22 (OH,F) 2 . Hornblende has a hardness of 5–6, a specific gravity of 3.0 to 3.6, and is typically an opaque green, dark green, brown, or black color. It tends to form slender prismatic to bladed crystals, diamond-shaped in cross section, or is present as irregular grains or fibrous masses. Its planes of cleavage intersect at 56° and 124° angles. Hornblende

100-476: Is a stub . You can help Misplaced Pages by expanding it . This article about a specific Canadian geological feature is a stub . You can help Misplaced Pages by expanding it . Hornblende Hornblende is a complex inosilicate series of minerals . It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole . Hornblende minerals are common in igneous and metamorphic rocks . The general formula

120-425: Is also common in igneous rocks, usually as a secondary mineral, formed by alteration of mafic minerals such as biotite , hornblende , pyroxene , or garnet . The glassy rims of pillow basalt on the ocean floor is often altered to pure chlorite, in part by exchange of chemicals with seawater. The green color of many igneous rocks, slates , and schists is due to fine particles of chlorite disseminated throughout

140-451: Is gray to white in color, and is named edenite from its locality in Edenville, Orange County, New York . Oxyhornblende is a variety in which most of the iron has been oxidized to the ferric state, Fe . Charge balance is preserved by the substitution of oxygen ions for hydroxide. Oxyhornblende is also typically enriched in titanium. It is found almost exclusively in volcanic rock and

160-431: Is most often confused with the pyroxene series and biotite mica , which are also dark minerals found in granite and charnockite . Pyroxenes differ in their cleavage planes, which intersect at 87° and 93°. Hornblende is an inosilicate (chain silicate) mineral, built around double chains of silica tetrahedra. These chains extend the length of the crystal and are bonded to their neighbors by additional metal ions to form

180-543: Is required. There is a solid solution series between hornblende and the closely related amphibole minerals, tremolite – actinolite , at elevated temperature. A miscibility gap exists at lower temperatures, and, as a result, hornblende often contains exsolution lamellae of grunerite . Hornblende is a common constituent of many igneous and metamorphic rocks such as granite , syenite , diorite , gabbro , basalt , andesite , gneiss , and schist . It crystallizes in preference to pyroxene minerals from cooler magma that

200-557: Is richer in silica and water. It is the principal mineral of amphibolites , which form during medium- to high-grade metamorphism of mafic to intermediate igneous rock (igneous rocks with relative low silica content) in the presence of pore water. Much of the pore water comes from the breakdown of micas or other hydrous minerals. However, hornblende itself breaks down at very high temperatures. Hornblende alters easily to chlorite , biotite , or other mafic minerals. A rare variety of hornblende contains less than 5% of iron oxide ,

220-534: Is sometimes called basaltic hornblende . The word hornblende is derived from German Horn ('horn') and blende ('deceive'), in allusion to its similar appearance to metal-bearing ore minerals. Chlorite group The chlorites are the group of phyllosilicate minerals common in low-grade metamorphic rocks and in altered igneous rocks . Greenschist , formed by metamorphism of basalt or other low-silica volcanic rock, typically contains significant amounts of chlorite. Chlorite minerals show

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240-458: The TOT layers of chlorite contain some aluminium in place of silicon, which gives the layers an overall negative charge. These TOT layers are bound together by positively charged O layers, sometimes called brucite layers. Mica is also composed of aluminium-rich, negatively charged TOT layers, but these are bonded together by individual cations (such as potassium, sodium, or calcium ions) rather than

260-521: The complete crystal structure. Hornblende is part of the calcium-amphibole group of amphibole minerals. It is highly variable in composition, and includes at least five solid solution series: In addition, titanium , manganese , or chromium can substitute for some of the cations and oxygen, fluorine , or chlorine for some of the hydroxide (OH). The different chemical types are almost impossible to distinguish even by optical or X-ray methods, and detailed chemical analysis using an electron microprobe

280-426: The element chlorine , also named from the same Greek root. Chlorite forms blue-green crystals resembling mica . However, while the plates are flexible, they are not elastic like mica, and are less easily pulled apart. Talc is much softer and feels soapy between the fingers. The typical general formula for chlorite is (Mg,Fe) 3 (Si,Al) 4 O 10 (OH) 2 ·(Mg,Fe) 3 (OH) 6 . This formula emphasizes

300-731: The mantle volume from which island arc magmas are generated. Clinochlore, pennantite, and chamosite are the most common varieties. Several other sub-varieties have been described. A massive compact variety of clinochlore used as a decorative carving stone is referred to by the trade name seraphinite . It occurs in the Korshunovskoye iron skarn deposit in the Irkutsk Oblast of Eastern Siberia . Chlorite does not have any specific industrial uses of any importance. Some rock types containing chlorite, such as chlorite schist, have minor decorative uses or as construction stone. However, chlorite

320-498: The range of chemical composition allows chlorite group minerals to exist over a wide range of temperature and pressure conditions. For this reason chlorite minerals are ubiquitous minerals within low and medium temperature metamorphic rocks, some igneous rocks, hydrothermal rocks and deeply buried sediments. The name chlorite is from the Greek chloros (χλωρός), meaning "green", in reference to its color. Chlorite minerals do not contain

340-512: The remaining chlorite, often with release of water vapor. Chlorite is one of the most common minerals produced by propylitic alteration by hydrothermal systems , where it occurs in the "green rock" environment with epidote, actinolite, albite, hematite , and calcite . Experiments indicate that chlorite can be stable in peridotite of the Earth's mantle above the ocean lithosphere carried down by subduction , and chlorite may even be present in

360-468: The rock. Chlorite is a common weathering product and is widespread in clay and in sedimentary rock containing clay minerals. Chlorite is found in pelites along with quartz , albite , sericite , and garnet , and is also found in associate with actinolite and epidote . In his pioneering work on metamorphic facies in the Scottish Highlands, G.M. Barrow identified the chlorite zone as

380-406: The structure of the group, which is described as TOT-O and consists of alternating TOT layers and O layers. The TOT layer ( T etrahedral- O ctahedral- T etrahedral = T-O-T ) is often referred to as a talc layer, since talc is composed entirely of stacked TOT layers. The TOT layers of talc are electrically neutral and are bound only by relatively weak van der Waals forces . By contrast,

400-455: The zone of mildest metamorphism. In modern petrology, chlorite is the diagnostic mineral of the greenschist facies. This facies is characterized by temperatures near 450 °C (840 °F) and pressures near 5 kbar. At higher temperatures, much of the chlorite is destroyed by reactions with either potassium feldspar or phengite mica which produce biotite , muscovite , and quartz . At still higher temperatures, other reactions destroy

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