TECHNIQUES based on the interference of polarised light have been used to investigate double refraction in transparent materials due to the structural anisotropy of crystalline solids and strain birefringence in amorphous solids1. Forrest and Marsh have discussed2,3 reflection methods and have used them to examine the anisotropy of the opaque solids carbons and cokes. As graphite is a uniaxial crystal with an optical c-axis perpendicular to the layer planes, polarised light incident on the layer-planes is not affected so that a polished section with this orientation appears isotropic. However, polarised light reflected by the prismatic faces is rotated and a polished section in this orientation shows optical anisotropy. By inserting a one wavelength retarder plate at 45° in front of the analyser of a polarising reflection-microscope with crossed polariser and analyser, interference colours are produced from which the orientation of the surface crystallites can be determined.