Hematite is the perfect heavy little substance. It's not as heavy, expensive or hard to shape as iridium. Nor is it pure. Just common iron oxide, solid, dark and - when polished right - lustrous as a field of stars. Somewhere in my effects is a little blob of milled hematite, a worry stone the size of my thumb. Until I find it, here is a string of hematite pearls from my wife's bead box. They are cold, and holding them, I could almost fall asleep.