For all of you rock collectors out there, here's a 3D-printable stand for your geode slices, up to 5/32 of an inch thick! Soon, I'll have more sizes for people with biger slices, and stands for your other rocks and minerals as well.

For slices 1/8 - 3/16 in. use the "rockholder" file.
For slices 1/4 in. use the "rockholder B" file.
For slices 5/16 in. use the "rockholder C" file.
Print using a raft.