So what do you do when you have a 12" thick block and need about 6"? Simple, use feathers and wedges to cleanly split the block and get it down to a reasonable size. In the video below, I show an easy way to very quickly split a block by drilling a few holes and then letting pressure do its work.
When I first started carving, If I needed to get rid of a lot of stone, I would get my point out and start chipping away. It would take me a great deal of time and I would waste a bunch of stone. Now, I break out a hammer drill and some feathers and wedges and I am able to cut the block in half and I have two useable pieces.