Hit it really hard with a hammer. Like as hard as you can. Only once or twice. It will also help to have as much supported by your hand/arm when you hit it. A pile of sand would also be a good way to help mitigate breaking where you don’t want it to break. There’s a reason people call it an art form. It takes time and a lot of practice. You can kind of use the claw on a normal hammer for this, but you should get a mason/brick hammer, or a geopick. I like Vaughn brick hammers the most, but it doesn’t really matter if you’re not going to be hitting rocks for the rest of your life.