It seems the vulcanite becomes grey/green, perhaps because of a strong utilisation: action of sweat, pressure on the body... But it's also a question of texture. I will make photos soon.
The grain is different too. We can find this vulcanite only between 34000 and 61000, very roughly speaking. We already had several discussions about the colour in the forum, Bill (?) showing that the colour had disappeared on the surface, but that black grains remained in the hollows.