BUT'TON-STONE, noun A species of figured stone, or hard flint, resembling a button, consisting of two bodies which appear to be the filling up of holes in a shell. A species has been found finely striated, like a mohair button. This name is given also to a species of slate found in the marquisate of Bareith.
Source: Webster's 1828 American Dictionary ↗ · public-domain · returned verbatim, no AI