I found some called magnet rocks at several of the local beach stores and they are various shapes.
I used them for the pull knobs on all of my overhead storage bins to hold the fold up doors open as needed.
They are a decorative look? For me anyway?
I have some that are flat circle,oblongs,small rectangles,squares ,triangle ish, and even a couple of heart shaped ones.
Thy are about a 1/2" thick.
I wanted to drill them and put a regular knob bolt through? But so far even a diamond bit for tile and glass won't even scratch them so liquid nail time consuming time it was to make them stay and look good and clean when the glue dried.
They were something like 10-for 2$ or something like that and my kids and I got to go through a bin of over 1000 to pick what we wanted.