Max Planck Institute for Dynamics and Self-Organization in Göttingen, Germany.
 Department of Physics,
University of Toronto, 60 St. George St., Toronto, Ontario, Canada M5S 1A7.
Ordered crack patterns are so common in Nature, that they are often overlooked. From cracks in ordinary mud to vast polygonal networks that stretch across the polar deserts of Earth and Mars, they are typical features in geomorphology. On a smaller scale, crack networks are also created for artistic effect on japanese raku pottery, and are found on the paintings of old masters. Cracking even determines the pattern of scales on the snouts of Nile crocodiles. The physics behind these patterns can be captured by requiring that cracks obey a simple elastic energy balance as they grow.