M. C. Domeneghetti

Kinetics of Fe2+-Mg distribution in aluminous orthopyroxenes

Kinetic studies of isothermal heating experiments (600–800° C) on aluminous pyroxenes (Mg0.942Fe0.8802+Fe0.0683+Mn0.016Ca0.010Al0.084) (Si1.848Al0.152) permit the determination of rate constant of isothermal disordering as 2.5457 E13(±1.4 E13) min−1. The activation energy is determined as 278 (±23) kJ/mol. Data on two other aluminous pyroxenes at 700° C indicate that the rate constant decreases significantly with increasing amount of trivalent cations. There is a similar but reverse correlation between the concentration of trivalent cations and the Fe2+-Mg equilibrium distribution between sites. The site distribution coefficient increases with increasing concentration of trivalent cations at constant temperature.

X-ray diffraction study of Fe2+-Mg order-disorder in orthopyroxene. Some kinetic results

AbstractKinetic rates of Fe2+-Mg disordering in three orthopyroxenes (mean value of XFe = Fe2+/(Fe2++Mg) = 0.175,0.482,0.770 respectively) have been determined employing heating experiments and single crystal X-ray structural refinements. Disordering rate constants

Thermal expansion behaviour of orthopyroxenes: the role of the Fe-Mn substitution

(\vec K)

Iron distribution in orthopyroxene: A comparison of Mössbauer spectroscopy and X-ray refinement results

(550800° C) for two pyroxenes are given by: ln

Phase transition and mixing behaviour of the cummingtonite-grunerite solid solution

(\vec K)

Strain and local heterogeneity in the forsterite-fayalite solid solution

= 27.107(±5.177)−32062(±783)T−1(XFe = 0.175) ln