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Amphiboles have long been key players in metamorphic petrology. The concept of facies was developed for rocks of basaltic composition (Eskola 1920, 1939; Fyfe et al. 1958), and within this concept, amphiboles had a leading role. The first appearance of amphiboles, the presence of amphiboles of certain compositions or last appearance of amphiboles that are replaced by pyroxene-bearing assemblages, mark a number of major facies boundaries. The transition from greenschist to amphibolite facies is marked, in part, by hornblende replacing actinolite, and the granulite facies is defined by the breakdown of hornblende to orthopyroxene-bearing assemblages. The blueschist facies is defined by the appearance of glaucophane, while the transition from blueschist-facies to eclogite-facies conditions is indicated by the breakdown of glaucophane to omphacitic pyroxene-bearing assemblages. References to amphibole names (actinolite, glaucophane) or rocks characterized by certain amphiboles (amphibolite/hornblende) figure prominently in six facies names (Turner 1981; Liou et al. 1985; Oh et al. 1988; Evans 1990; Peacock 1993). A large part of the literature that is devoted to metamorphic petrology of amphiboles concerns reactions which produce amphiboles from more hydrated mafic igneous rocks or lead to the destruction of amphiboles as they break down to form anhydrous or nearly anhydrous mineral assemblages. Consequently, amphiboles can be thought of as occupying the wide intermediate portion of P-T- Xfluid space in which metamorphic rocks are found.
The number of citations of the published amphibole nomenclature serves as a yardstick (meterstick?) of the interest in amphiboles and a minimum estimate of the amount of literature devoted to this mineral. Two versions of the nomenclature of amphiboles have appeared: 1978 and 1997 (Leake 1978; Leake et al. 1997), and they have been cited a over 2300 times in the past 28 years. This works out to a minimum …