Cutting marble that doesn't cut. Whether you are using nippers or a hammer and hardie, if the piece of stone you are attempting to cut is not cutting then move the stone further out from under the blades.
Look at the drawing here, it is a front on drawing of a hammer over a piece of marble on the hardie. As you can see the hammer blade does not cover all of the marble piece. Remember, although we talk about cutting we do not cut stone, we are sending a fracture through it.
By moving the blades further off the stone we are focusing the energy from the strike of the blade to a smaller area. This then means more power goes to a smaller area.
Always use tools as if you were just going to be using them every day for the next 10 years. Use the safest, most effective, most economical of your energy techniques that you can.