Rotten stone

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(Min.) a soft stone, called also Tripoli (from the country from which it was formerly brought), used in all sorts of finer grinding and polishing in the arts, and for cleaning metallic substances. The name is also given to other friable siliceous stones applied to like uses.

See also: Rotten

References in periodicals archive ?
Part of the restoration work involved cutting back half an inch of rotten stone from the front wall.