Stone is weird, the surface prep varies so widely, as does the grain structure. Its hard to generalize, and is usually covered under porous/nonporous. If smooth, lightly abrade any polished surfaces if practical, and ca should work fine when gaps are <1mm, use baking soda to fill gaps qnd build up edges. For rough/porus, use a 2-part epoxy of your desired properties, all major brnds are great. It can be helpful to knock down tall spots to get better contact of the surfaces to be joined. Making a regular series of gouges can increase surface area for stronger mechanical bonds.
