Amphibole - wikipedia Amphibole This article is about the mineral. For the logical fallacy, see equivocation. For the ambiguous grammatical construction, see amphibology. For the study of amphibians ( amphibiology ), see amphibian. This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( November 2010 ) Amphibole ( Tremolite ) Amphibole ( / ˈæmfɪboʊl / ) is the name of an important group of generally dark - colored, inosilicate minerals, forming prism or needlelike crystals, composed of double chain SiO 4 tetrahedra, linked at the vertices and generally containing ions of iron and / or magnesium in their structures. Amphiboles can be green, black, colorless, white, yellow, blue, or brown. The International Mineralogical Association currently classifies amphiboles as a mineral supergroup, within which are two groups and several subgroups. Contents 1 Mineralogy 1.1 In rocks 2 History and etymology 3 Mineral species 3.1 Chemical formula 3.2 Descriptions 4 See also 5 Notes 6 References Mineralogy Amphiboles crystallize into two crystal systems, monoclinic and orthorhombic. In chemical composition and general characteristics they are similar to the pyroxenes. The chief differences from pyroxenes are that ( i ) amphiboles contain essential hydroxyl ( OH ) or halogen ( F, Cl ) and ( ii ) the basic structure is a double chain of tetrahedra ( as opposed to the single chain structure of pyroxene ). Most apparent, in hand specimens, is that amphiboles form oblique cleavage planes ( at around 120 degrees ), whereas pyroxenes have cleavage angles of approximately 90 degrees. Amphiboles are also specifically less dense than the corresponding pyroxenes. In optical characteristics, many amphiboles are distinguished by their stronger pleochroism and by the smaller angle of extinction ( Z angle c ) on the plane of symmetry. Amphiboles are the primary constituent of amphibolites. In rocks Amphiboles are minerals of either igneous or metamorphic origin ; in the former case occurring as constituents ( hornblende ) of igneous rocks, such as granite, diorite, andesite and others. Calcium is sometimes a constituent of naturally occurring amphiboles. Those of metamorphic origin include examples such as those developed in limestones by contact metamorphism ( tremolite ) and those formed by the alteration of other ferromagnesian minerals ( hornblende ). Pseudomorphs of amphibole after pyroxene are known as uralite. History and etymology The name amphibole ( Ancient Greek ἀμφίβολος - amphíbolos meaning ' ambiguous ' ) was used by René Just Haüy to include tremolite, actinolite, tourmaline and hornblende. The group was so named by Haüy in allusion to the protean variety, in composition and appearance, assumed by its minerals. This term has since been applied to the whole group. Numerous sub-species and varieties are distinguished, the more important of which are tabulated below in two series. The formulae of each will be seen to be built on the general double - chain silicate formula RSi O. Four of the amphibole minerals are among the minerals commonly called asbestos. These are : anthophyllite, riebeckite, cummingtonite / grunerite series, and actinolite / tremolite series. The cummingtonite / grunerite series is often termed amosite or brown asbestos ; riebeckite is known as crocidolite or blue asbestos. These are generally called amphibole asbestos. Mineral species Chemical formula Orthorhombic series Anthophyllite, ( Mg, Mg ) Si O ( OH ) Holmquistite, Li Mg Al Si O ( OH ) Ferrogedrite, Fe Al Si O ( OH ) Monoclinic series Tremolite, Ca Mg Si O ( OH ) Actinolite, Ca ( Mg, Fe ) Si O ( OH ) Cummingtonite, Fe Mg Si O ( OH ) Grunerite, Fe Si O ( OH ) Hornblende, ( K, Na ) ( Ca, Na, Fe, Mg ) ( Mg, Fe, Al ) ( Al, Si ) O ( OH ) Glaucophane, Na ( Mg, Fe ) Al Si O ( OH ) Riebeckite ( or Crocidolite ), Na Fe Fe Si O ( OH ) Arfvedsonite, Na Fe Fe Si O ( OH ) Richterite, Na Ca ( Mg, Fe ) Si O ( OH ) Pargasite, NaCa Mg Fe Si Al O ( OH ) Winchite, ( CaNa ) Mg ( Al, Fe ) Si O ( OH ) Edenite, NaCa Mg ( Si Al ) O ( OH ) Descriptions On account of the wide variations in chemical composition, the different members vary considerably in properties and general appearance. Anthophyllite occurs as brownish, fibrous or lamellar masses with hornblende in mica - schist at Kongsberg in Norway and some other localities. An aluminous related species is known as gedrite and a deep green Russian variety containing little iron as kupfferite. Hornblende is an important constituent of many igneous rocks. It is also an important constituent of amphibolites formed by metamorphism of basalt. Actinolite is an important and common member of the monoclinic series, forming radiating groups of acicular crystals of a bright green or greyish - green color. It occurs frequently as a constituent of greenschists. The name ( from Greek ἀκτίς, ἀκτῖνος / aktís, aktînos, a ' ray ' and λίθος / líthos, a ' stone ' ) is a translation of the old German word Strahlstein ( radiated stone ). Glaucophane, crocidolite, riebeckite and arfvedsonite form a somewhat special group of alkali - amphiboles. The first two are blue fibrous minerals, with glaucophane occurring in blueschists and crocidolite ( blue asbestos ) in ironstone formations, both resulting from dynamo - metamorphic processes. The latter two are dark green minerals, which occur as original constituents of igneous rocks rich in sodium, such as nepheline - syenite and phonolite. Pargasite is a rare magnesium - rich amphibole with essential sodium, usually found in ultramafic rocks. For instance, it occurs in uncommon mantle xenoliths, carried up by kimberlite. It is hard, dense, black and usually idiomorphic, with a red - brown pleochroism in petrographic thin section. See also List of minerals Classification of minerals - Silicates http://media-2.web.britannica.com/eb-media/53/2653-004-DB6D5422.gif Notes Jump up ^ `` Amphibole ''. Dictionary of Geology. Retrieved 2013 - 01 - 21. Jump up ^ Mindat, Amphibole Supergroup ^ Jump up to : One or more of the preceding sentences incorporates text from a publication now in the public domain : Spencer, Leonard James ( 1911 ). `` Amphibole ''. In Chisholm, Hugh. Encyclopædia Britannica. 1 ( 11th ed. ). Cambridge University Press. pp. 883 -- 884. Jump up ^ US Geological Survey, Asbestos, accessed 20 July 2015. References C. Michael Hogan. 2010. Calcium. eds. A. Jorgensen, C. Cleveland. Encyclopedia of Earth. National Council for Science and the Environment. Cornelius S. Hurlbut and Cornelis Klein. 1985. Manual of Mineralogy, 20th ed., John Wiley and Sons, New York ISBN 0 - 471 - 80580 - 7 GND : 4160663 - 2 NDL : 00564762 Retrieved from `` https://en.wikipedia.org/w/index.php?title=Amphibole&oldid=802650604 '' Categories : Inosilicates Asbestos Hidden categories : Wikipedia articles incorporating a citation from the 1911 Encyclopaedia Britannica with Wikisource reference Wikipedia articles incorporating text from the 1911 Encyclopædia Britannica Articles needing additional references from November 2010 All articles needing additional references Wikipedia articles with GND identifiers Talk Contents About Wikipedia Asturianu Беларуская Български Català Čeština Dansk Deutsch Eesti Ελληνικά Español Esperanto Euskara فارسی Français Gaeilge Galego 한국어 Հայերեն हिन्दी Hrvatski Bahasa Indonesia Italiano עברית ಕನ್ನಡ Қазақша Lietuvių Nederlands 日本 語 Norsk nynorsk Oʻzbekcha / ўзбекча Polski Português Română Русский Slovenčina Slovenščina Srpskohrvatski / српскохрватски Suomi Svenska Українська Tiếng Việt 中文 Edit links This page was last edited on 27 September 2017, at 15 : 31. 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Question: the most common member of the amphibole group
Answer: Amphiboles