A GEM in the rough!
AE As (30mm, 11.85g, 6h). Rome mint, struck 86, interstitial issue.
IMP CAES DOMIT AVG GEM COS XII CENS PER P P, head laureate right, with aegis; IOVI CONSERV, Jupiter standing left, with thunderbolt and scepter, S C in field.
RIC 489 var, obverse inscription GEM.
Another case of curing bronze disease. What a plague that is, either turns the coin into a heap of green dust or else it comes out looking like this after treatment! Oops, back in treatment! What a nightmare!