Abstract
SUMMARY: Magnetite grains in lateritic saprolite have altered in situ to porous hematite (martite) grains. Hematite occurs as relatively large (∼ 1 μm) platy crystals, triangular arrays of small (0.01–0.05 μm) lathlike crystals and very small (< 100 Å) platy anhedral particles. Titanium increased in altered grains and may substitute for Fe3+ in hematite. Mn, V, Cr and Zn remained approximately constant whereas the Ni content decreased. Halloysite crystallized from soil solution within pores resulting in a marked increase in the Si and Al contents of grains.