Yes, it looks like a tetradrachm minted in Alexandria. It should be around 18-20mm but thicker than average for a Roman coin.
It is definitely thicker than the average Roman coin, size about the same of a quarter... The head on the reverse looks like Zeus?
Its Serapis, a kind of made up God combining many cultures ideals. Btw, I was wrong earlier, it should be more like 22-24mm.
Thanks much, medoraman! I guess the tricky part now is trying to identify who's the emperor on the reverse