Basalt columns: Large scale constitutional supercooling?

The conventional interpretation of basalt column formation in terms of cracking of a homogeneous magma during cooling is questionable because cooling cracks in homogeneous materials do not tend to form quasi-hexagonal patterns. It is proposed that basalts develop inhomogeneous patterned compositions during cooling as a result of constitutional supercooling. The latter is observed in metallic alloys, and its mechanism is briefly described. It is expected to produce a quasi-hexagonal pattern of glassy interfaces. These interfaces crack preferentially during uniaxial cooling. (C) 2009 Elsevier B.V. All rights reserved.