The cairn isn't the summit, as the undulating moor on Grit Fell doesn't have one readily-identifiable highest point. According to the Ordnance Survey, it reaches 468 m asl... somewhere.
The rock in the foreground is Carboniferous millstone grit (of the Ward's Stone Sandstone formation), but it's hardly unique to Grit Fell and I doubt that's the source of the name.
Blaze Moss is ~8¾ km behind the cairn, curving round to Holdron Moss on the right. The hill beyond that ridge is Totridge, overlooking the Trough.