A polymorph of Al(OH)3 that occurs in bauxites and soils and rarely in dolomitic marls. Nordstrandite is a two-layer, dioctahedral structure of Al octahedra (similar to layers found in gibbsite), but with displacements between the layers. Ideally, adjacent layers are superposed in bayerite, offset in nordstrandite, and reversed in gibbsite, presumably because of strong polarization effects of the OH.
Cf., gibbsite, bayerite