MINERALS/Amphiboles 503 the secondary one is based on cation size, and the tertiary one is based on structure; uranyl sulphates, chromates, molybdates/wolframates, and thiosulphates are in separate subdivisions In Class 8, the primary subdivision is based on the presence or absence of additional anions and H2O, the secondary one is based on cation size and OH:H2O ratio, and the tertiary one is based on crystal structure Separate subdivisions are reserved for uranyl phosphates and arsenates and for polyphosphates, polyarsenates, and polyvanadates (with V in fourfold coordination) In Class 9, the primary subdivision is based on the degree of polymerization of the SiO4 tetrahedra in the structure; the secondary one is based on the presence or absence of additional anions, the coordination number of the cations, and, in certain cases, on the periodicity of the polymerized units Tertiary subdivision is based on crystal structure Zeolites are in a separate division and are further subdivided on the basis of structure The minerals of Class 10 are divided into acetates, oxalates, benzine salts, hydrocarbons, and miscellaneous organic minerals See Also Analytical Methods: Mineral Analysis Further Reading Bayliss P (2000) Glossary of Obsolete Mineral Names Tucson: The Mineralogical Record Inc Blackburn WH and Dennen WH (1997) Encyclopedia of Mineral Names The Canadian Mineralogist, Special Pub lication Ottawa: Mineralogical Association of Canada Clark AM (1993) Hey’s Mineral Index, 3rd edn London: Chapman & Hall Gaines RV, Skinner HCW, Foord EE, et al (1997) Dana’s New Mineralogy, 8th edn New York: Wiley and Sons Johnsen O (2002) Minerals of the World Princeton, NJ: Princeton University Press Kampf A and Gerhold G (eds.) (1998) The Photo Atlas of Minerals CD format Los Angeles: Gem and Mineral Council, Los Angeles County Museum of Natural History Klein C (2002) The Manual of Mineral Science, 22nd edn New York: John Wiley & Sons Lima de Faria J (2001) Structural Classification of Minerals, vol 1: Minerals with A, AmBn and ApBqCr General Formulas Dordrecht: Kluwer Academic Publishers Lima de Faria J (2003) Structural Classification of Min erals, vol 2: Minerals with ApBqCrDs to ApBqCrDsExFyGz General Formulas Dordrecht: Kluwer Academic Publishers Lima de Faria J (2004) Structural Classification of Min erals, vol 3: Minerals with ApBq .ExFy .nAq General Chemical Formulas and Organic Minerals Dordrecht: Kluwer Academic Publishers Mandarino JA and Back ME (2004) Fleischer’s Gloss ary of Mineral Species 2004 Tucson: Mineralogical Record Inc Martin RF (ed.) (1998) The Nomenclature of Minerals: A Compilation of IMA Reports Ottawa: Mineralogical Association of Canada Nickel EH and Grice JD (1998) The IMA Commission on New Minerals and Mineral Names: procedures and guidelines on mineral nomenclature, 1998 Canadian Mineralogist 36: 14 Strunz H and Nickel EH (2001) Strunz Mineralo gical Tables, 9th edn E Stuttgart: Schweizerbart’sche Verlagsbuchhandlung (Naă gele u Obermiller) Amphiboles R A Howie, Royal Holloway, University of London, London, UK ß 2005, Elsevier Ltd All Rights Reserved The minerals of the amphibole group differ from the pyroxenes (see Minerals: Pyroxenes) in having a double-chain silicate structure and in having hydroxyl ions as an essential constituent Their name is from the Greek amphibolos (ambiguous) in allusion to the great variety of compositions and appearances shown by this mineral group All have a perfect {210} cleavage, and typically range from white to yellow, green and dark green, or blue, the coloured varieties having variable to strong pleochroism As in the pyroxene group, both orthorhombic and monoclinic amphiboles occur; their flexibility of ionic replacement is due to their structure The composition of the simplest calcium-rich amphibole, tremolite, may be expressed by the formula Ca2 Mg5 ẵSi8 O22 OHị2 , the Ca atoms occupying the largest positions of between six- and eight-fold coordination The general chemical formula for an amphibole can be given as A0 B2 C5 ½T8 O22 ðOH; FÞ2 where A represents the larger cations, B the cations in M4, C the cations in M1, M2, and M3, and T those in the T1 and T2 sites (Figures and 2) The four main substitutions seen in the amphibole structures are: