They may be a toe. Or an oar. Or a fishing hook.

I've exhausted every avenue I can think of trying to evaluate the substance--things like mass, specific density, specific heat capacity, x-ray spectrosopy angles, lattice configurations... Don't let this go too far but I get inconsistencies at best and complete nonsense at worst. But then again, I was only measuring in qualities that would be implied in four dimensions. If these things are cross-sectional geometry of something in a borderworld or even straight out of one, then that would explain it!