Clinopyroxene from Brazilian kamafugites

The composition of pyroxenes from the two occurrences of kamafugites in Brazil — Santo Antônio da Barra and Mata da Corda — was investigated with the aim of comparing the localities and characterizing kamafugitic pyroxenes in general. Kamafugitic pyroxene is always diopside, except for late phases that can be richer in aegirine. In relation to their silica content, Mata da Corda and Santo Antônio da Barra pyroxenes are different: the former are similar to Italian kamafugitic pyroxenes, lamproitic and orangeitic pyroxenes, having higher Si contents in the tetrahedral site; whereas the Santo Antônio da Barra pyroxenes are similar to African kamafugitic pyroxenes. Both are more enriched in IVAl than other kamafugitic pyroxenes. In Santo Antônio da Barra and Mata da Corda pyroxenes, the Al content is not always sufficient to fill the tetrahedral site and Si substitution by Fe3+ is required. There is a general trend of enrichment in Ti, Na and Fe3+ with the evolution of crystallization in both Mata da Corda and Santo Antônio da Barra pyroxenes, especially in ugandites. The main substitutions present in these Brazilian pyroxenes are Ca(Mg,Fe)Si2O6 by CaTiAl2O6, NaTiAlSiO6 and Na Fe3+ Si2O6 end-members. The main conclusion is that it is not possible to distinguish the compositional range of clinopyroxene from orangeites, lamproites, and kamafugites.