Like most things it is all technique. The first thing I can tell you is that pounding perpendicularly down on it will not get you far. Rock is strongest in compression.
We had an exercise in the engineering corps where a boulder half that size but granite was brought in while we were away one day and each platoon had a chance to have a go at it to get it moved. Considering that there were over 300 of us, only with hand tools, that rock got bludgeoned something silly for over 8 hours and all we had were a few splinters and a lot of people who needed bandaging. Once all the brute force had been worn out, a few intellectuals remained, who had stood back during "the show".
You really have to look carefully to find the shear planes and work accurately to split the rock by wedging between the natural laminations or fracture lines. A 2lb hammer and a handful of sharp chisels will do the job. Obviously, you want to try to split chunks off near the surface. Once you are breaking of layers 3" thick you can be bolder and try for thicker, but beware, the softer the rock, the less likely it will work. With the granite we first got a few slabs off maybe an inch thick, then 3" and finally we were getting chunks off 6" thick or more. But that stuff is brittle. One had to be dead nuts on the orientation/alignment of the point of the chisel to the "fault line", else all you got was dust.
Slow down, take some time and look real careful at the surface and avoid the "sheer force" mentality. I can assure you that the Egyptians and the people on Easter island had only hand tools and hew all those giant blocks and slabs out of solid rock and there was definitely some technique involved.
