1911 Encyclopædia Britannica/Holystone
HOLYSTONE, a soft kind of sandstone used by sailors for scrubbing and cleaning the decks of ships. The origin of the word is doubtful. Some authorities hold that it arose from the general practice of scrubbing the decks for Sunday service; while others think the name arises from the fact that the stone so employed is naturally porous and full of holes. A small flint or stone having a natural hole in it, and worn as a charm, is also called a holystone.