Tepetate

Where erosion has reduced the soil layer to less than planting depth or to exposed tepetate, farmers may break up and pulverize the tepetate with plows, picks, crowbars, sledgehammers, or even black powder, to form a usable soil layer.

Alternating dry and wet periods may favour crystallisation of amorphous aluminium silicates to phyllosilicate clays, so that many tepetates have clay coatings that are due to recrystallisation rather than to clay illuviation (see also Chapter 12).

Tepetate is a vernacular Mexican term referring to a hardened land with various degrees of infertility. Tepetates are derived from volcanic material, mainly tuff. The scientific definition reserves the term tepetate for a hardened layer in soils formed from pyroclastic materials. In the Central Valley of Mexico these indurate layers are among the most striking geological features.