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.
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Con il contributo del Ministero per i Beni e le Attività Culturali