Luminescence of Orthopyroxenes

Abstract

IN an examination of several stony meteorites Derham and Geake¹ reported on the luminescence of three enstatite achondrites under proton excitation. A later report² concludes that enstatite, the major mineral in the meteorites, is probably responsible for all the observed luminescence. Each meteorite yields a spectrum in which red emission with a peak at 6700 Å is accompanied by a weaker blue peak at 4000 Å. The red peak at 6700 Å in meteoritic enstatite has been attributed by Garlick³ to MgSiO₃ containing manganese as an impurity. Sarver and Hummel⁴ have shown that both photo- and cathodo-luminescence occur in the red spectral region (6310–6830 Å) of Mn-activated magnesium germanates and silicates. The position of peak emission of enstatite activated with Mn(II) is extrapolated from MgGeO₃–MgSiO₃ enstatite solid solutions to be 6730 Å. This is near the value found in synthetic clinoenstatite activated with Mn(II), namely, 6720 Å. By examining crushed grains of the Bustee meteorite, Derham, Geake and Walker² were able to separate grains which luminesced blue from a mixture in which most of the grains luminesced red. The luminescence spectrum of the ‘blue’ grains differs from that of the ‘red’ grains and from the luminescence spectrum of the meteorite in that the red peak at 6700 Å is weaker than the blue peak at 4000 Å. X-ray powder analyses of ‘red’ and ‘blue’ grains showed both to be orthoenstatite.