Pleasant little automation game! The web version ends on diamond, and it took me ~5 minutes to get up to it due to refining buildings working instantaneously.
If you're looking to take this further and make it more of an incremental game, you could add a timer to refinement and create some kind of loop where materials get a little better each time rather than instantly being improved. It would incentivize using the splitters so there's still some passive income while making the refinement process take longer and longer each time.Otherwise great game as is!