The inner core is now known to be elastically anisotropic [ Woodhouse et al., 1986; Tromp, 1993]. Jeanloz and Wenk [1988] identified the inner core's anisotropy with the plastic deformation-induced anisotropy of hcp iron. Karato [1993] has suggested that aniostropy of the inner core could be explained if there is anistropy of magnetic susceptibility of the iron crystal structure. Presuming the cubic structure of iron is magnetically isotropic, then the hexagonal phase of iron is preferred in the core. However, Stacey [1992] points out that the core may be elliptical in shape if rotation leads to preferential deposition of inner core material, causing the inner core to deform towards its equilibrium flattening. Crystal alignment would result from the deformation.
Kumazawa et al. [1992] proposed that the inner core grows nonuniformly in either of two possible spatial patterns with axial symmetry (somewhat similar to the Stacey hypothesis), producing seismic anisotropy. Thus it is not conclusive that an anisotropic core results from anisotropic crystal structure. The inner core anisotropy does not guarantee an hcp inner core.