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.