Re: clay, laterite and vermiculite

Neil Frank says....
>A consistent definition of this 
>mystical product would be useful, but I have not been able to find one.  I 
>once checked with soil science professor from NC State University who had 
>travelled extensively thru the tropics and he said there is not such 
>thing as laterite.  I seem to remember that he used the term latersoil. 

Agriculture Canada holds a document called "Formation of Laterite", 1979.
It lists and gives a synopsis of 49 scientific articles on the development
of laterite in various parts of the world. So the term and the soil type
exist. Most of the terms used are Greek to me. Fe2O3,SiO2, and Al2O3 seem
to be the important constituents of laterite and their proportions vary
according to the type. There is talk of concretionary and alveolar
laterites etc. Some quotes.....

Laterites are formations consisting of ferruginous quartz and occurring
as friable concretions or as concretions cemented together into a compact
mass (laterites proper).

...the Fe in plinthite is present as hematite, amorphous hydroxides, and

Gibbsite is the main mineral of tropical laterites,...

Strong absorption of organic anions by amorphous ferric hydroxide...
Absorption of phosphate, molybdate or silicate by ferric hydroxide...

The upper part of laterite formed on crystalline schists contained
in Northern Vietnam
58.85%  SiO2
0.55%   SO3
0.03%   P2O5
13.5%   Al2O3
25.82%  Fe2O3
0.22%   CaO
0.32%   MgO
0.23%   K2O
0.05%   Na2O
0.80%   TiO2
& traces of Mn
Further down in the soil the iron is reduced to about 6%.