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Licensed Unlicensed Requires Authentication Published by De Gruyter April 2, 2015

Solution calorimetric investigation of fluor-chlorapatite crystalline solutions

Guy L. Hovis and Daniel E. Harlov
From the journal American Mineralogist

Abstract

Solution calorimetric measurements have been made on 17 synthetic fluorapatite-chlorapatite crystalline solutions at 50°C in 20.0 wt% HCl under isoperibolic conditions. Analysis of the calorimetric data indicates that heats of mixing across the series may reach values as high as 8.3 kJ/mol. Normally such a high degree of thermodynamic nonideality would be associated with immiscibility, yet no such miscibility gap is indicated by either synthetic or natural fluor-chlorapatite specimens. Based on full chemical analyses, all Cl-rich samples (XCl > 0.65) of this study have halogen deficiencies that imply the presence of 4-11 mol% vacancies in the anion sites, which are interpreted to be associated with oxyapatite substitution. Separate analysis of data for the vacancy-free samples produces a linear fit for enthalpy of solution vs. composition, which yields an alternative interpretation of thermodynamic ideality. Together these models define the limits of enthalpy behavior for the fluor-chlorapatite system

Received: 2009-12-30
Accepted: 2010-3-14
Published Online: 2015-4-2
Published in Print: 2010-7-1

© 2015 by Walter de Gruyter Berlin/Boston