Evidence of graphite from the Onverwacht series Precambrian cherts, Swaziland system of South Africa

Examination of insoluble organic matter by X-ray diffraction has revealed the presence of graphite in a number of chert and carbonate samples from the Kromberg Formation of the Onverwacht Group (more than 3.2·109 years old). In one sample, shear stress appears to have given rise to modified rhombohedral graphite, indicating that the Lower Onverwacht may have been metamorphosed.