502 MINERALS/Definition and Classification of Minerals (1950) has gone through three editions In Hey’s classification, minerals are divided into 32 main categories that are subdivided into smaller groupings on the basis of predominant cations Most of the other classification systems combine the criteria of chemical composition and crystal structure The system used by the International Centre for Diffraction Data (1993) categorizes the minerals into 177 groups based on crystallographic criteria; the groups are divided into subgroups on the basis of chemistry and/or crystallography The principal groupings in Fleischer’s Glossary of Mineral Species (1999) are similar, but lack the subgroupings In the system advocated in 1983 by Lima-de-Faria (Table 2), minerals are divided into aqueous and nonaqueous categories; these are then subdivided on the basis of element ratios and then on the basis of crystal-structure type In the Dana system (Table 3), minerals are divided into 22 categories, based mainly on anion composition, except for the silicates, which comprise six categories based on polymerization of the SiO4 tetrahedra Further subdivision of the nonsilicates is based primarily on composition, whereas Table Principal categories in the classification system of Lima de Faria Category Type Minerals without water molecules in their structure A AmBn ApBqCr ApBqCrDs ApBqCrDsEx ApBqCrDsExFy ApBqCrDsExFyGz ApBqCrDsExFyGz ApBq ExFy n (aq.) Minerals with water molecules in their structurea a Work on this category is in progress that of the silicates is based on the configuration of the SiO4 units The Strunz system (Table 4), probably the most widely used classification system, divides minerals into 10 classes, based on anion composition Further subdivisions are based on chemical and structural criteria, which are different in each of the classes In Class 1, the primary subdivision is based on composition and the secondary one is based on structure In Class 2, the primary subdivision is based on composition (chiefly the cation/ion ratio), the secondary one is based on further compositional criteria, and the tertiary one is based on structure In Class 3, the primary subdivision is based on composition (principally on the compositional complexity and the presence or absence of combined H2O), the secondary one is based on cation:anion ratio, and the tertiary one is based on structure In Class 4, the primary subdivisions are based on cation:anion ratio and the presence or absence of H2O, with separate subdivisions for the uranyl hydroxides, vanadates with 5- or 6-coordinated V atoms, and arsenites, antimonites, bismuthites, sulphites, selenites, tellurites, and iodates Further subdivisions are based on cation size and structure type In Class 5, the carbonates are subdivided first on the presence or absence of additional anions and H2O, secondly on cation size, and ultimately on crystal structure The nitrates are subdivided on the basis of the presence or absence of OH and H2O In Class 6, the primary subdivision is based on the number of borate units in the chemical formula and the secondary one is based on structure In Class 7, the primary subdivision is focussed on the presence or absence of additional anions and H2O, Table system Class Table Principal categories in the Dana classification system Native elements and alloys Sulfides and related compounds Oxides Halogenides Carbonates Nitrates Iodates Borates Sulphates Selenates and tellurates; selenites and tellurites Chromates Phosphates, arsenates, and vanadates Antimonates, antimonites, and arsenites Vanadium oxysalts Molybdates and tungstates Organic compounds Nesosilicates: insular SiO4 Sorosilicates: isolated tetrahedral noncyclic groups, N > Cyclosilicates Inosilicates: two dimensionally infinite silicate units Phyllosilicates Tektosilicates 10 Principal categories in the Strunz classification Description Elements (metals and intermetallic alloys; metalloids and nonmetals; carbides, silicides, nitrides, phosphides) Sulphides and sulphosalts (sulphides, selenides, tellurides; arsenides, antimonides, bismuthides; sulpharsenites, sulphantimonites, sulphbismuthites, etc.) Halides Oxides (hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulphites, selenites, tellurites, iodates) Carbonates (ỵ nitrates) Borates Sulphates (selenates, tellurates; chromates, molybdates, wolframates) Phospates, arsenates, vanadates Silicates (germanates) Organic compounds