Rough diamond octahedral. Photo Bjorn Wylezich via Dreamstime.
Diamonds are best known today in their colorless cut form seen in countless jewelry stores. However, they look considerably different when they come out of the ground. They’re not always lovely in that state. But one interesting and common shape of diamond rough is the octahedron. It looks like two pyramids stacked base to base. (Well, actually, as you can see in the photo, they’re often kind of plump and rounded pyramids.)