Bricks, Masonry, Asphalt and Concrete - burn marks on bluestone hearth

We have a one-piece hearth made of bluestone. Over time, burning embers, etc have fallen onto the hearth and left black marks. I was able to clean off the actual soot with a wire brush and a cleaner called "M-1". However, i cannot clean the purplish marks on the bluestone that are still present under where the soot was. Are these actual burn marks in the stone? How can they be removed? I have also tried bleach and a muriatic acid solution without success. Someone had mentioned hydrogen peroxide (35%). Does this sound like it would work?
Thanks.Dave

Sorry, but I don't think removing the scorching is possible. Hydrogen peroxide or a stronger bleaching agent like oxalic acid (wood bleach) may lighten it if applied in poultice form. The scorching is similar to the chemical process that a brick undergoes in a kiln. For more on poultices see the doityourself.com how to pages. If necessary a stone restoration specialist may be able to carve the section out then fill it with matching material.