Silver State Quarters

If you really want to be sure use the tissue paper test. Just lay a single layer of tissue paper over the coin in the holder and look at it. If it is silver the coin will show as a white circle. Is it is clad it will show as a dull gray. Try it with a couple of known coins first. You will be amazed at the amount of difference in the appearance of the two coins through the tissue paper. This is a great test because it can be used on the coins without removing them from their holders, either slabs or government holders. (You're not likely to find many sellers who will let you open the government holders and take out the coins to check the edges to make sure they haven't been swapped.) About the only way this might fail is if someone silver plates a clad coin, but if they do that it would possibly damage the mirrors and be noticeable that way.