Journal of Petrology | Volume 1 | Number 1 | Pages 218-260 | 1960
© Oxford University Press 1960
research-article |
The Geochemistry of Scapolite Part I. Previous Work and General Mineralogy
Department of Geology, McMaster University Hamilton, Ontario, Canada
ABSTRACT
The literature on the mineralogy and petrology of the scapolite family is reviewed. The general formula was examined in the light of 126 analyses from the literature, together with 9 new analyses. Of these 135 analyses, refractive indices were available for 64. Sixty-four of the analyses were rejected as unsatisfactory, 46 were classed as dubious, and 35 were accepted as satisfactory. In the absence of complete structural information the following formula was established as provisionally suitable:
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where W is mainly Ca, Na, and K, but may include small amounts of other metals; Z is Si and Al, often with excess Si and deficient Al, but sometimes the reverse; R is (a) CO3, SO4, O2H2, Cl2, or F2, for meionite components, or (b) Cl, F, HCO3, HSO4, or OH, for marialite. The nomenclature is accepted as marialite, Meo-Me20; dipyre, Me20-Me50; mizzonite, Me50-Me80; meionite, Me80-Me100. Pure marialite does not occur in nature and 80 per cent Ma is the maximum attained.
The relations between average index and birefringence with composition were investigated. A determinative chart showing average index versus per cent. Me was constructed, but the variation of birefringence with composition is more complex and cannot yet be used for accurate determination of scapolite composition. Variation of density with per cent Me also shows poor correlation.