pebblestone

In popular usage, a roundish stone of any kind from the size of a nut to that of a man’s head. In a philosophical sense, minerals distinguished from flints by their variety of colors, consisting of crystalline matter debased by earths of various kinds, with veins, clouds and other variegations, formed by incrustation round a central nucleus, but sometimes the effect of a simple concretion. Pebbles are much used in the pavement of streets. A general term for water-worn minerals.