this is an interest concept i haven't come across before but makes senseCrystal Cautions
This page contains geological data that cautions one when using certain types of crystals/minerals. While most in the metaphysical/spiritual community only speak of the higher purpose properties, common sense must be taken into consideration when using these on a physical level. This page is a cautionary measure on stones that may be harmful in certain situations or specific types of minerals (raw versus tumbled, Fibrous versus crystallized or mass) , whether it be in Elixirs or prolonged holding, bathing, touching to skin, etc.
It is not meant to perpetuate fear or anxiety, but instead to educate and share our deep respect for the crystal and mineral kingdom. Most on the list are geared toward internal use with a few being cautionary for external use. A good rule of thumb is to make sure you wash your hands after using any crystal/mineral. It keeps our mineral friends clean and is a great way to show respect to ourselves and our crystal/mineral family.
Pay particular attention to the list when you are working with raw/natural specimens. I do not think tumbled stones, for the most part, would be harmful, with a few exceptions, such as Realgar.
NOTE: Before making any elixir or charging any water, it is a good idea to double check for any possible toxicity that may occur, if using several stones in combination, for elemental reactions between the stones. In fact, it would be best if each stone charges in its own container of water as opposed to putting four or five stones in the same container.
If you have any doubt, simply place the crystal/stone around and outside of the container.
a list follows at the link
http://www.healingcrystals.com/Crystal_Cautions_Articles_1009.html