I worked with high-end epoxy products for aerospace applications for over 30 years. The key to long-lasting joints is to carefully prepare the surface by sanding or sand-blasting, then degrease with a solvent like acetone, if possible apply and cure a compatible primer, then apply the epoxy adhesive. Some pressure is needed to create a thin, uniform bond line and squeeze out air pockets, if possible.
When bonding stone, you could also heat the part to advance the cure - even low temperatures would help.
Many of the original epoxies were very brittle, but now most have toughening agents added. I researched this a bit when I needed a reliable, room temperature cure epoxy and I recommend Gorilla clear 5 minute epoxy. As indicated in Frank's post, museums have epoxies that won;t yellow with age(very common).
You need to take some care to measure out the quantities of the two components correctly but if the material hasn't "gone bad" with age, the ratio of the two parts can be off somewhat and you can still get a good cure.
If I needed to make beads like the ones shown - I would bond together stone layers as a big sandwich in a press to get thin bond lines, using some heat and a top end epoxy. After the cure I'd slice the block into blanks and proceed with shaping into beads. In my industry we used saws with gang blades to slice out a bunch of pieces with one pass. A production line could be set up to fabricate these types of beads very quickly and theoretically could be mostly automated.