What is a "Holystone"? Why was it called a "Holystone?
Please leave your answer in the comments below:
A holystone is soft sandstone, often used to scrub the decks of ships. Sailors had to kneel as if in prayer when scrubbing the decks. Holystone was often called so because it is full of holes.
As Frank says in his comments below, think 'olde tyme' sandpaper.