Our contractor laid down a tile on our renovated bathroom and somehow did not realized that it was defective (see picture). The defect is some sort of metal mineral (kind of rough) the kind that would hurt if you are walking barefoot and step on it. We noticed it before it was groutted but told the contractor the following day but by then it was already grouted.
Can anyone suggest a solution to how to polish/remove that mineral part without making too much damage to the tile? We have not yet put the sealant solution onto the tiles.
Any suggestions will be greatly appreciated.