The mineralogy of nickel-bearing laterite deposits is poorly understood, with conflicting structural models for their nature and co-ordination.
Currently there is a simple three-fold classification for nickel-bearing laterites, based on largely empirical criteria:
There are conflicting structural models for the nature and co-ordination of nickel within both layer silicates and iron oxy-hydroxides.
In laterite oxide zones the bulk of nickel is accommodated in variably crystalline goethite, where the Fe3+-for-Ni2+ substitution in goethite must be accompanied by a mechanism to compensate the charge imbalance.
Nickel substitution is probably accompanied by hydroxylation, however it is also possible that co-substitution on Ni2+ with other polyvalent ions such as Mn and Cr may be the cause.