A cobalt-rich spinel inclusion in a sapphire from Bo Ploi, Thailand

Cobalt-rich spinel is found as a ~200 μm inclusion, together with a glassy phase, in a gem-quality blue sapphire from Bo Ploi, Thailand. Its composition is directly analogous with that of cochromite, a previously reported rare cobalt-rich chromite. Transition elements decrease in abundance from core to rim of the spinel while the other elements increase. Crystal chemical considerations suggest that a vacancy-creating substitution mechanism may be operative in the cobalt-rich spinel. The glassy phase coexisting with the spinel is likely to be the product of heating by the host basaltic magma. -from Authors