I am away from my references, and I do not recall from memory if this
type was issued in
billon. If it was, this may be a silver-plated
billon coin. The easiest way to tell would be to grind a point on the edge on a testing
stone. If you see fresh copper on the inside, then you will know that the coin is not silver after all.
This was an issue a few years back with some mysterious "silver"
billon aspron trachy coins of Isaac II that turned out to be ordinary issues with thick silver plating.