An Introduction to Environmental Chemistry

110 Chapter Four

100

0 2000 4500

Rainfall (mm)

Percentage of soil

Smectite

Kaolinite

Gibbsite

Fig. 4.18The influence of climate on clay mineralogy in Hawaii. The relatively rapid water

flow rates associated with high rainfall result in the preferential removal of cations and silica.

After Sherman (1952).

Fe, Al

oxides

Depth Smectite

Gibbsite

Kaolinite

Clay mineral

Leaching

Si : Al

CIA

0 : 1

1 : 1

2 : 1

0 100

Fresh basalt

substrate

Fig. 4.19Idealized vertical distribution of clay minerals formed under leaching conditions in

soils developed on basalt. CIA values increase from 30–40 in fresh rock to near 100 in heavily

leached surface soils.