rottenstone

noun

A soft decomposed limestone, used in powder form as a polishing material.

To polish with rottenstone.

noun

An argillaceous or silicious limestone which by weathering has become soft and friable, the calcareous part having been wholly or in part removed.

noun

A soft, friable limestone, used in polishes

noun

a weathered and decomposed siliceous limestone; in powdered form it is used in polishing