ho·ly·stone 
(hōlē-stōn′)
(hōlē-stōn′)n.
A piece of soft sandstone used for scouring the wooden decks of a ship.
tr.v. ho·ly·stoned, ho·ly·ston·ing, ho·ly·stones
To scrub or scour with a piece of soft sandstone.
[Perhaps from a sailor's kneeling position while scouring with the stone.]