see laterite

(mineral): A mineral formed in the soil profile at the water-table when iron-oxides accumulate and cement together to form a gravelly or nodule-rich band. This may become impervious to water (cf. duplex). When exposed it is popularly used for gravel roads. Also known as hardpan, ironpan, laterite, ouklip or ngubane.

Ferricrete is a mineral conglomerate consisting of surficial sand and gravel cemented into a hard mass by iron oxide derived from the oxidation of percolating solutions of iron salts. The word is derived from the combination of ferruginous and concrete.