IT'll take some real researching, I'm pretty sure there is some sort of metal content in the rock that forms the crystaline structures... what element(s) I've no clue. On the other hand all land rock is formed from some sort of metals, Guess we've have a need for a geologist, or maybe just a good elemental composition of the rock... google or maybe even wikipedia? The one element you NEED to avoid is copper in any form, I'm sure there are others but Cu is a definate.