Weathering rind

A broken basalt cobble (15 x 10 cm size) showing well-developed weathering rind from Brazil, where chemical weathering is quite active.
Weathering rind of a large granite glacial erratic eroding out of unconsolidated Permian till, Selwyn Rock, Inman Valley, South Australia

A weathering rind is a discolored, chemically altered, outer zone or layer of a discrete rock fragment formed by the processes of weathering. The inner boundary of a weathering rind approximately parallels the outer surface of the rock fragment in which it has developed. Rock fragments with weathering rinds normally are discrete clasts, ranging in size from pebbles to cobbles or boulders. They typically occur either lying on the surface of the ground or buried within sediments such as alluvium, colluvium, or glacial till. A weathering rind represents the alteration of the outer portion of a rock by exposure to air or near surface groundwater over a period of time. Typically, a weathering rind may be enriched with either iron or manganese (or both), and silica, and oxidized to a yellowish red to reddish color. Often a weathering rind exhibits multiple bands of differing colors.[1][2][3]

Although sometimes confused with weathering rinds, spheroidal weathering is a different type of chemical weathering in which spherical layers of weathered material progressively develop in situ around blocks of jointed bedrock beneath the Earth's surface, rather than in reworked and transported clasts such as cobbles and boulders.[4][5]

  1. ^ Colman, SM, and KL Pierce (2001) Weathering rinds on andesitic and basaltic stones as a Quaternary age indicator, Western United States. Professional Paper no. 1210. United States Geological Survey, Reston, Virginia.
  2. ^ Neuendorf, KKE, JP Mehl, Jr., and JA Jackson, eds. (2005) Glossary of Geology (5th ed.). Alexandria, Virginia, American Geological Institute. 779 pp. ISBN 0-922152-76-4
  3. ^ Oguchi, CT (2001) "Formation of weathering rinds on andesite." Earth Surface Processes and Landforms. 26(8):847–858.
  4. ^ Fairbridge, RW (1968) Spheroidal Weathering. in RW Fairbridge, ed., pp. 1041-1044, The Encyclopedia of Geomorphology, Encyclopedia of Earth Sciences, vol. III. Reinhold Book Corporation, New York, New York.
  5. ^ Ollier, CD (1971). Causes of spheroidal weathering. Earth-Science Reviews 7:127-141.