Fig. 2

a Photographs of both sides of the triangular grindstone fragment from layer RGS2 (square C4d); b, c high magnification images of residues exhibiting various red hues and d the characteristic Raman spectra obtained on the grindstone; (A) haematite, (B) maghemite and anatase (142 cm⁻¹), (C) amorphous carbon (1608 and 1372 cm⁻¹) and quartz (467 and 130 cm⁻¹), (D) manganese oxide and haematite (only the bands at 224, 292 and 406 cm⁻¹ are observable) and (E) anatase