Elephant Skin Weathering
May 23, 2013
Photographer: David K. Lynch; Dave's San Andreas Fault Web site
Summary Author: David K. Lynch
Many massive carbonate rocks like limestone, marble and dolomite show elephant skin weathering, so called because of its resemblance to the rough, weathered hide of elephants. This weathering starts out as minute, random cracks in the rock that are exposed to rainwater. Rainwater is slightly acidic because atmospheric carbon dioxide (CO2) dissolves in water (H2O) to form carbonic acid (H2CO3). This slightly acidic rainwater then seeps into the cracks and dissolves a thin layer of limestone, converting it to calcium bicarbonate. The bicarbonate remains in solution and runs off, thereby leaving an enlarged crack. Over many years, the cracks deepen and widen, resulting in the aptly named surface. Elephant skin weathering in found almost exclusively on fine-grained carbonate rocks.
These specimens were found in the Soda Mountains near Baker, California. Notice that the rock fractured and broke along one of the enlarged cracks (missing fragment next to the penny). Photo taken on April 27, 2013.
Photo details: Camera Model: PENTAX K-x; Lens: smc PENTAX-DA 18-250mm F3.5-6.3 ED AL [IF]; Focal Length: 142.5mm (35mm equivalent: 214mm); Aperture: f/8.0; Exposure Time: 0.0050 s (1/200); ISO equiv: 1600; Software: K-x Ver 1.00.