We report the synthesis of a wide range of single-crystal spinel platelets with exposed (111) faces, lateral dimensions in the micrometer range, and thicknesses of 20-50 nm, prepd. by soft chem. dehydration of well crystd. layered precursors. This method enables the synthesis of the metastable compn. NiCoAlO₄, which cannot be prepd. by conventional solid state synthesis. Because of their nanoscale thickness, mosaic structure, shape anisotropy, and surface porosity, NiCoAlO₄ and NiCo₂O₄ platelets exhibit room-temp. superparamagnetism (T_B = 40 and 250 K, resp.) despite the fact that they have micrometer-size lateral dimensions. The accessibility of a wide range of superparamagnetic spinel platelets (as opposed to cubes or spheres) should be useful for studies in ferrofluids and related composite magnetic materials. [on SciFinder(R)]