I have an OMC and I was taking some pictures today and noticed this with the macro lens. I've read about bruted girdles particularly on older cut stones but I'm not sure if that is what I'm looking at here?
Yes, that is a very old-style bruted girdle. The 'hairlines' running into the facets, we call that beard, a defect resulting from very old-technology bruting and reduced-attention workmanship. The way the facets do not come together are another indicator of the stone being truly old, probably cut well before the advent of better controllable cutting-equipment.