Heat capacity and thermodynamic properties for coesite and jadeite, reexamination of the quartz-coesite equilibrium boundary

Abstract

Single-crystal and powder X-ray diffraction data were collected to characterize the macroscopic solid-solution and cation-ordering behavior in the system augite-jadeite (low acmite content). We examined 28 natural pyroxenes with compositions on the join augitejadeite and with different degrees of order. Annealing experiments were carried out to obtain crystals with different degrees of order (P2/n) and complete disorder (C2/c) at compositions between 35 and 60% Jd. Three synthetic C2/c pyroxenes with composition Di 80 Jd 20 , Di 60 Jd 40 , and Di 50 Jd 50 were also examined.