Fluorine in sarcolite: additional history and new chemical data

Abstract

AbstractThe historical background leading to the discovery of sarcolite by Thomson is reviewed. Many mineralogical reference works quote Thompson (1807) but no paper on sarcolite by Thomson has been found; also the spelling of Thomson is incorrect on numerous occasions. The history of sarcolite from its original discovery is reviewed. Chemically, sarcolite is inadequately characterized in spite of a structural study by Giuseppetti et al. (1977). All known chemical analyses are collated and discussed. Two new analyses, using a combination of gravimetric, colorimetric, atomic absorption, and electron probe methods, are presented which show sarcolite to contain 2 wt. % flourine. The presence of this element in sarcolite was reported in 1860 but no quantitative data given; the new determinations cast some doubt over certain aspects of the sarcolite structure.Measured densities of sarcolite range from 2.93 to 2.96 (mean 2.95) gm/cm3; the tetragonal unit cell of a 12.32 and c 15.48 Å leads to a calculated density of 2.925 gm/cm3 using the empirical formula. Empirically sarcolite may be expressed as:Na1.38Ca6.0(Ca0.37,K0.13,Fe0.08,Sr0.07,Mg0.05)Σ0.70 Al3.90Si6.02P0.54O26.20F1.06C0.06and ideallyNa2Ca12(Ca,K,Fe,Sr,Mg)2Al8Si12(P,Si)O52F2and suggests 27 (oxygen and fluorine) atoms in the quarter unit cell.Details are given of the mineralogical assemblage, optical properties, infra-red and thermal behaviour of sarcolite which, after 176 years, is still known from only one locality—Monte Somma.