Pebble
From Wikipedia, the free encyclopedia
A pebble is a clast of rock with a particle size of 4 to 64 millimeters based on the Krumbein phi scale of sedimentology. It is generally described to be larger than gravel and smaller than cobble. A rock made predominantly of pebbles is termed a conglomerate. Pebble tools are among the earliest known man-made artifacts, dating from the Palaeolithic period of human history. They have been found at Olduvai Gorge (1.85 million years ago[citation needed]) and at Longuopo in China (1.8 to 1.5 MYA[citation needed]).
A beach composed chiefly of surface pebbles is commonly termed a shingle beach, which has armoring characteristics with respect to wave erosion; moreover, this type of beach has unusual ecological niches that may provide habitat for a number of rare and endangered species.
