Piemontite schists from Haast River, New Zealand

Abstract

SummaryPiemontite-bearing metachert horizons are recorded from regionally metamorphosed eugeosynclinal rocks at Haast River, in the Southern Alps of New Zealand. Piemontite schist mineralogical assemblages produced by epidote-amphibole facies metamorphism are described petro-graphically, and are compared with lower grade occurrences in the Haast Schist Group.A chemical analysis yields a composition of (Ca1·75Mg0·02Mn0·25Na0·03K0·01) (Al2·23Fe0·53Mn0·24 Ti0·01)Si3·06O12(OH)0·9, which is compared graphically with other metamorphic, hydrothermal, and metasomatic piemontites.Single-crystal Weissenberg and powder camera X-ray data are given, and an attempt made to relate these X-ray parameters to chemical variation within the piemontite composition range.