How do I remove this stain? (Picture)

[jenbendy]

This is on the black slate around my fireplace. Will not come off. Not sure if it's damage from water dripping out from flower vase, or heat from large candle. Think it's the vase and a water stain.

Any ideas how I remove it?

If it's from water then it could be limescale. In which case I'd use dilute white vinegar - spray on, leave a couple of minutes then wipe off.

Pink stuff? Be careful though as it slightly abrasive

Have bought a black polish kit and will try that