Because of the expertise involved, this is not a job for a do it yourselfer. You need a qualified stone mason. The first thing they'll do is assess your current fireplace. If it's made out of stone or concrete, they can build right over it. If it's drywall, the mason will have to add some metal lath and scratch coat to the wall to give the stone something solid to stick to. If you have a good structurally sound hearth, it can stay. But if it's lightweight, it won't hold the stones and the mason will have to build a new one. If you have tile or marble around your fireplace, the mason will have to take it down.
Most jobs will take two to three days. The first day consists of tearing down the materials around the old fireplace and putting up the metal lath and scratch coat. That needs to dry for 24 hours.
The next day the masons will start laying out the stones. They start on the hearth and build up. They do this because the hearth will take the load from the stones on both sides. The 2x4 that holds up the mantle will take the weight of the stones in the middle of the wall.
They dry-fit the stones on the hearth before setting them in thin set and mortar. They make sure to mix the larger stones with the small ones to make it look like a jigsaw puzzle.
The stones we used were from a quarry called Vengeance Creek in North Carolina. They're 450 years old and are made out of metaphorphic quartzite which creates beautiful earth tone colors.
The cost is about $20 a square foot, which is less expensive than most man-made stones.