SOIL FORMATION - Soil Ecology - page 164

Table II.4 summarises the major chemical weathering processes. The minerals that
form in hot and humid tropical environments are typically kaolinite and goethite and,
at the wetter extremes, gibbsite. In warm areas with alternating wet and dry seasons,
smectites are typically the dominant clay minerals. Degradation rather than neoformation
is typical of temperate climates and incompletely altered minerals such as exfoliated
illite and chlorite, irregular mixed layers, vermiculite and degraded smectites are
characteristic. In the cold areas of the high latitudes and altitudes and in the arid areas of
the world, hydrolysis is limited by the lack of water. Few necformed clays are formed
and the clay sized materials present consist largely of the minerals also present in the
parent rocks. The broad scale patterns given above are modified by local conditions of
relief, poor drainage, salt accumulation and other factors.
Figure II.3 presents a highly generalised map of the dominant weathering processes
occurring in different parts of the world. This is based on the four major weathering
types recognised by Pédro and Sieffermann (1979) and also indicates the largely
ice-covered continents of Antarctica and Greenland where appreciable chemical
weathering is limited to the non ice covered areas.
The dominant weathering processes in the acidolytic area are acidolysis and acido-
complexolysis and are associated largely with the cold humid environments of North