The weird white stone

Unloading the washing machine just now, I found the following items in that rubbery seal part where things always get stuck: a pen with Darthvader on it, a grey tissue, a hairclip and a white stone. The first three items I put in the bin as they were all beyond redemption. The white stone, however, is a frequent visitor to my w/m, in fact I can't count the times I've found it in there. So, not wishing to evoke the wrath of any evil spirits, I put it back in.