In geology, a boulder (or rarely bowlder)[1] is a rock fragment with size greater than 25.6 cm (10.1 in) in diameter.[2] Smaller pieces are called cobbles and pebbles. While a boulder may be small enough to move or roll manually, others are extremely massive.[3] In common usage, a boulder is too large for a person to move. Smaller boulders are usually just called rocks or stones.
^Webster's New International Dictionary of the English Language. Springfield, Massachusetts: G. & C. Merriam Company. 1913.
^Neuendorf, K.K.E.; Mehl, J.P. Jr.; Jackson, J.A., eds. (2005). Glossary of Geology (5th ed.). Alexandria, Virginia: American Geological Institute. p. 79. ISBN978-0922152896.