Another thing to look for is the edge. If you see it is the same solid color as the rest of the coin it is silver. If you see it is a copper color, and the remainder of the coin does not have this whitish appearance, its copper nickel clad. The "Red Book" suggested by DigginThePast, is generally updated annually. It won't be dead on the money as far as retail values for coins, but it gives you a fair ballpark. If you want something closer for US coins, I would suggest you suscribe to the "Grey Sheet". This same one is used by many good reputable coin dealers.