Seemed like a really nice strike, fairly well centered and nicely toned. Obv: IMP GORDIANUS PIUS FEL AUG Rev: IOVI STATOR Jupiter facing right holding scepter and thunderbolt. "To Jupiter, who upholds and preserves" According to my research Jupiter was the premier deity over all other Roman gods of the time and similar to Zeus in Greek mythology. As for silver purity in this one, they say at this time various mints were producing various fineness from 37% to 43% silver. I think these are fairly common. I paid on the higher side for the toning but seller sent a very nice gift with it for a delay.
Beautiful coin - I have speculated that the celators who responsible for the beautiful coins of Caracalla were either still alive during the reign of Gordian III or they passed on their knowledge. Certainly the regular issues of the Rome mint managed to make beautiful coins up to the reign of Volusian when the need to work fast finally resulted in problems.
