Hi Jesse - since these shapes are actually intended to be faceted objects, this is one of the few cases where using the "MeshToNurb" command in Rhino will work really well.

To convert it, don't bother with extracting points, just select the mesh stone, run MeshToNurb on it in Rhino, and export the resulting NURBS model.

This will convert each polygonal face into a (potentially trimmed) NURBS surface.

- Michael