IN an attempt to extend the scope of palaeomagnetism when investigating endogenous geological processes1,2 the magnetic properties of high-temperature minerals were investigated. The main objective was to find other minerals not yet examined from this point of view which would be amenable to palaeomagnetic examination. The Japanese work on pynthetic ferrites3 suggested to us that certain natural high-temperature minerals (possessing a high isomorphic miscibility of elements) might have similar lattice structures and in consequence be ferromagnetic and capable of retaining a stable thermo-remanent magnetization. The investigation proved successful. Garnets were the obvious minerals for initial examination. All the garnets examined possessed a weak ferromagnetic moment of the order 10−5 E.M.U./C.C., but were found to be unstable and so of little use in palaeo-magnetism. Of a number of other minerals examined, cassiterite was found to possess unique palaeomagnetic properties.