The heat from the gas makes the slate go white.

We bought a Ryland Home in late January and have a black slate gas fireplace. The mantel, sides and hearth were replaced for the 2^nd time Tuesday, May 2^nd, 2006 and we were told to not touch it for two days before cleaning it up. Today after said cleaning with water we noticed there are two long grooves that appear to be scrapes in the slate coming straight out from the gas fireplace center. Is there something that can be used to fill or buff these out. The installer told us to keep lemon oil on the slate to give it the new shine look. Is there something else that can be used that will stay on? The heat from the gas makes the slate go white in less than a week. We would appreciate any advice you can give us.