Re: Laterite Question

> From: Pat Bowerman <bowerman at specent_com>
> Date: Sat, 09 Dec 1995 18:44:52 -0800
> A couple of questions, for all of our soil gurus out there, how does
> laterite differ from the reddish clay commonly found in the southern
> U.S. ?
> What makes laterite,...laterite? 
> Is it the % of oxidized iron that it contains, or is there some other
> unique property or element?
> Why does it occur only in tropical areas?

Here's what a net source said lo these many years ago.  I hope it's
correct because I've been repeating it on the net and in print for
quite a while now :-).

| From: girard at ecs_umass.edu
| Date: Wed, 11 Dec 1991 23:47:29 GMT
| In regards to the inquiry of whether any clay can be used to fertilize
| (or supplement) aquarium plants: Laterite is technically a residual
| clay, meaning that many many^many centuries eons, etc when the clay
| formed, it formed in an environment that was stable geologically.
| While the clay just sat there, weathering took place, and lots of
| changes occurred.  Specifically, ion exchange happened, where ions of
| calcuim, magnesium, iron, potassium, sodium etc were adsorbed
| (absorbed- can't remember which is applicable) into the clay
| particles.
| Residual clays are found in the Southern US (Georgia red clay, for
| example) in addition to South America.  "Regular" clays may not be
| suitable, since most clays in the US are not weathered residual clays
| (too much erosion, glaciers etc.)  Most clays, ie montmorillonite,
| illite, kaolinite etc. etc.  are composed of silica and alumina
| compounds. In residual clays, the silion, but more often the aluminum
| ions are replaced with the beneficial (to plants) ions like Fe, Mg,
| Ca.
| In addition to all this, certain clays have a high cation exchange
| capacity, meaning, certain ions are readily adsorbed.  In other clays,
| like kaolinite (which is white, an indication of the lack of
| "contaminants") there is practically no ion exchange capacity.  Color
| is a good indication of ion exchange red/brown clay has alot of iron,
| white/gray clay may not have much of anything useful.  Of course,
| montmorillonite has a very high cation exchange capacity, and in the
| "pure" form is pale gray, but I'm sure if you took mont. and mixed
| fine iron filings in it and made a soup out of it and cooked it for a
| while, you'd get some ion exchang occurring.  Note, that is not a
| suggestion, just an abstract possibility.
| BTW, I am a Geotechnical Engineering grad student - I study "dirt" I
| am one with the soil, and all that. :-)
| Jeff @ UMass
George in Spring-like Colorado