Nomenclature of the amphibole supergroup

Abstract

A new classification and nomenclature scheme for the amphibole-supergroup minerals is described, based on the general formula AB(2)C(5)T(8)O(22)W(2), where A = square, Na, K, Ca, Pb, Li; B = Na, Ca, Mn2+, Fe2+, Mg, Li; C = Mg, Fe2+, Mn2+, Al, Fe3+, Mn3+, Ti4+, Li; T = Si, Al, Ti4+, Be; W = (OH), F, Cl, O2-. Distinct arrangements of formal charges at the sites (or groups of sites) in the amphibole structure warrant distinct root names, and are, by implication, distinct species; for a specific root name, different homovalent cations (e.g., Mg vs. Fe) or anions (e.g., OH vs. Fe2+) are indicated by prefixes (e.g., ferro-, fluoro-). The Classification is based on the A, B, and C groups of cations and the W group of anions, as these groups show the maximum compositional variability in the amphibole structure. The amphibole supergroup is divided into two groups according to the dominant W species: (w)(OH,F,Cl)-dominant amphiboles and O-w-dominant amphiboles (oxo-amphiboles). Amphiboles with (OH, F, Cl) dominant at W are divided into eight subgroups according to the dominant charge-arrangements and type of B-group cations: magnesium-iron-manganese amphiboles, calcium amphiboles, sodium-calcium amphiboles, sodium amphiboles, lithium amphiboles, sodium-(magnesium-iron-manganese) amphiboles, lithium-(magnesium-iron-manganese) amphiboles and lithium-calcium amphiboles. Within each of these subgroups, the A- and C-group cations are used to assign specific names to specific compositional r…