Polishing Granite or Basalt

Quoted text begins.Did you use any acid in the polishing process? I once used hydrochloric
acid to remove tool marks from a textured area and oaxcilic acid in final
polishing and ended up with a clouding effect on Portoro Marble.
End of quote.

John, rain was naturally acid even before cars and steel mills became
commonplace. This is because carbon dioxide mixes with the falling drops,
particularly during a thunderstorm: http://pubs.usgs.gov/gip/acidrain/2.html

Of course, pollution makes the marble deteriorate faster, in company with water,
UV radiation and heat.

Basalt and granites are unaffected by most acids (one exception being
hydrofluoric acid). Polishing of basalt and granite is carried out using tin
oxide compounds which are microabrasives with no chemical action at all.

Any stone composed of calcium carbonate will be affected by acids. Oxalic acid
is used in the final polishing process of marble because it reacts with calcium
carbonate to form a layer of calcium oxalate on the stone's surface. If it is
not used carefully, oxalic acid can also remove the polish.

Could your clouding be bruising or scorching? Bruising is caused by mechanical
stress (hammering) during texturing, when the marble crystals are shattered
below the surface. Scorching is caused by heat stress, when honing stones or
buffing pads dry out and burn the crystals.

Simon