After reading this I went out and searched amongst the "river rocks" used for landscaping and drainage around our apartments. After a few minutes I discover a small piece of eroded limestone (6cm x 4cm x 2cm) with an almost circular 5mm hole straight through the middle. So now I have my own "hag stone" and can sleep peacefully...
There's a Greyhound station in Mississippi or Alabama or someplace with a mural in the terminal with a macabre limerick about the hare's foot not being lucky for the bunny. I saw it 15 years ago, no doubt it's gone by now.
Surprising to see such a thorough article incorrectly spell "loadstone" instead of "lodestone". Must be over-enthusiastic autocorrect.