Determination of olivine and serpentine in kimberlite by X-ray diffraction

Abstract

Olivine and serpentine in kimberlite from the Wesselton pipe have been quantitatively determined by a modified X-ray diffraction procedure in which concentrates of the minerals were separated from the kimberlite for use as analytical standards. The olivine extracted was essentially mono-mineralic but the serpentine contained 25% olivine as finely disseminated inclusions. Equations were deduced to interrelate measured X-ray diffraction intensities with the mineral content and particle size distributions of ground kimberlite samples and standards. Particle size distributions were characterised by means of appropriate absolute size constants. For Wesselton kimberlite containing about 35 and 48% of olivine and serpentine, respectively, a relative precision of 6% was achieved. The total olivine and serpentine content (83%) agreed well with that determined by particle-point counting (88%) and thin-section microscopy (83%).