Considering that you say you found them near an old quarry, they most probably are rock-crusher balls (also called Mill-balls, because they are used in a Tumbler Mill to turn chunks of stone into gravel).
That judgment is particularly supported by the limestone powder encrusted on them.
However, you can clean off the rust-encrustion, then measure them precisely with a caliper, and weigh them precisely on a Postal Shipping scale (bathroom scales are too inaccurate), and see if there is an exact matchup for their size and weight here: www.civilwarartillery.com/shottables.htm