I just bought 40 sq ft of tumbled stone for use as a backspash in my kitchen. I noticed some portions of the boxes are wet and the inside of the boxes has black stuff (not sure if they are mold) Some stones have lots of holes or pits that have black stuff in them, bu I am not sure if it that's something I should be concerned or it's just a part of the natural look of the tumbled stone. If those black stuff are mold, is there something I can clean it with and still be safe for use? I don't know if the dealer will take it back. Even if I they take them back for an exchange, they might just transfer the tumbled stone in a nice clean box to make it look like a fresh batch. So how do I know if those are really mold? Thank you so much for your time.