Model pyroxenes III: Volume of C2/c pyroxenes at mantle P, T, and x

Abstract

Variations in unit-cell volumes of mantle minerals as functions of P and T are important parameters in the description of the interior of the Earth and the behavior of materials. Recently, Thompson and Downs (2004) presented a model for the crystal structures of pyroxenes parameterized in terms of the O3-O3-O3 angle, θ, and the oxygen radius, r. This model has proven useful in the analysis of compression and expansion mechanisms in pyroxenes, providing an understanding of θ and r as functions of P and T. However, it did not provide a basis for analyzing changes in some properties that are strongly dependent on composition.