I have a wood burning fireplace with a firebrick hearth that continues into the firebox as the floor. I saw an home improvement show that covered a firebrick hearth and firebox floor with granite. Is this OK? Any other material that could be used? While the sides of the surround are of stone masonry, the top is wood. I'd really like to have the hearth and top of the surround of the same material. To make it easier to clean, I'd like to continue the hearth material into the firebox. Any suggestions?

The hearth and surround may be covered with marble, granite or slate but I'm not sure about the fire box. Are you sure the hearth is firebrick?. Usually a hearth is not firebrick.