Slate lost its color & has white chalky look to it

I have a slate floor.  This room flooded about a year ago and what appear to be water marks/stains are left.  A white outline around where a rug was remains, underneath where the rug was still looks glossy and bright and where the carpet was not has lost its color and has a white, chalky look to it.  Is it possible to restore the color to this flooring and is there anything I can use to remove the white chalky look.  I have been told everything from strippers, to acid to paint thinners but do not want to do anything to further damage the slate.  Thank you.