Remember this soaking method cleaning tip for marble countertops? If you have a marble fireplace, you can do the same thing to help get rid of soot. Here's how:
To bring back the nice, non-sooty finish of your marble fireplace, DIY Life suggests applying hydrogen peroxide to a wash cloth and leaving it overnight to soak with a little tape or pressure from an additional item. It's a quick and labor free method to keep your marble looking its best. Check out more details over at DIY Life.