Holystone is a soft and brittle sandstone that was formerly used in the Royal Navy and US Navy for scrubbing and whitening the wooden decks of ships.

A variety of origins have been proposed for the term, including that such stones were taken from broken monuments of St. Nicholas Church in Great Yarmouth or else the ruined church of St. Helens adjacent to the St Helens Road anchorage of the Isle of Wight where ships would often provision. The US Navy has it that the term may have come from the fact that 'holystoning the deck' was originally done on one's knees, as in prayer. Smaller holystones were called "prayer books" and larger ones "Bibles". Holystoning eventually was not generally done on the knees but with a stick resting in a depression in the flat side of the stone and held under the arm and in the hands and moved back and forth with grain on each plank while standing or partially leaning over to put pressure on the stick-driven stone. Holystoning continued on teak-decked Iowa class battleships into the 1990s.