Rocks n boulders break with very little effort using explosives. I've popped a couple just using a powder blast ( not legal, don't attempt..)
As we all know were limited to hand tools and no explosives, but that doesn't mean you can't crack a large rock.
I've been able to successfully break and move large boulders with hand tools like chisels and leaf spring wedges to make a split across a line in the rock. There's a few tutorials on it. I'd suggest using an electric drill as each hole can take up to an our if drilling by hand.
..will quickly add, that bloke has a few interesting and informal bids I'm pretty sure! Thanks for reminding me!