Looks like it could have been silvered bronze due to a light silver color on some parts which can not be seen in the photo. It also makes a high tone when dropped on a hard surface. My guess is the it might be bronze with a low alloy of silver. A contemporary counterfeit would be very cool, more interesting and less generic than a regular Antoninianus. Looks struck, no seam or anything either. Maybe a homemade die that an ancient counterfeiter made.
some cool "only ancients". time to get them coins some company boys, ancient coins don't like to be alone!