Studi sperimentali sui pirosseni onfacitici: sintesi idrotermali a moderate pressioni. Parte I. Soluzioni solide $CaMgSi_{2}O_{6} \rightleftharpoons Na(Cr,Fe^{3+})Si_{2}O_{6}$

Bondi, Mirella ; Morten, Lauro ; Mottana, Annibale

Atti della Accademia nazionale dei Lincei. Rendiconti della Classe di scienze fisiche, matematiche e naturali, Série 8, Tome 71 (1981) no. 5, pp. 101-114

Résumé

Experimental studies have been carried out at $P(H_{2}O)$ 1 to 2 kbar and temperatures 500 to 800 °C on coprecipitated gels in the systems diopside-acmite (Di—Ac) and diopside-kosmochlor (Di—Ko) with the purpose of determining the solid solution properties. The Di—Ac system is binary under the conditions used, and the unit-cell parameters of the intermediate compositions appear to vary in an appreciably linear way. For Fe-rich compositions, however, the time factor is essential in controlling the synthesis experiments, given the tendency of $Fe^{3+}$ to become reduced to $Fe^{2+}$, so that non-stoichiometric pyroxenes form. The Di—Ko system displays a very limited range of solid solution ( 5% $Ko$), which casts doubts on the possibility that $Ko$ may play a significant role in the crystal chemistry of chromiferous diopsides and/or omphacites occurring in high-pressure kimberlite nodules.