I am setting up a naturalistic terrarium and want to incorporate some rock work to hide pots and the area at the base of the terrarium where I syphon out excess water. I bought 100% natural slate (the shale mulch type used in garden for decoration) and I am washing it very clean. I am finding its pretty mucky but it appears to be just powdery slate fines. It's washing off dark grey no signs of soil. Once clean will it be safe?
Terrarium will be dominated with Heliamphora, a few highland Nepenthe, Australian and African sundew, Mexican Pings and Utricularia. Plus lots of moss.