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Re: Laterite and clay

On Sun, 24 Jan 1999, Bob Dixon wrote:

> I thought laterite WAS
> clay.  That's why kitty litter works as a good (to some folks anyway)
> substitute.  It definitely IS clay, at least the cheap, no-clump, no-deodorant
> stuff we are supposed to be using is.
> So set me straight here, okay?  Thanks

Laterite is a heavily leached tropical subsoil.  When exposed and dried it
sometimes is rock-like.  It isn't a fertile soil.  Laterite consists
usually of aluminum oxyhydroxides with smaller amounts of iron
oxyhydroxides and a little bit of a clay mineral called halloysite.
Silica, calcium, magnesium, potassium and sodium are present in very low
amounts or absent.  In some instance the iron content of laterite can
exceed the aluminum content, but even small amounts of iron will tint the
laterite rust red.  Phosphate has a strong tendency to attach to the iron
hydroxides present in most laterites.  The laterite may have a small
cation or anion exchange capacity, but I don't think this is an inherent
property of the material.

The material marketed as laterite may or may not be real laterite but I
suspect that most of it actually is laterite.

Clay may refer to any very fine-grained soil.  Clay soils are made up
mostly of a group of very finely crystalline minerals (grain size
typically << 2 microns) that are collectively called clay minerals.  There
are also varying amounts of organic materials, iron and aluminum
hydroxides and silica. A clay used for ceramic work is composed largely of
clay minerals.  Clay minerals are complex aluminosilicates with an
inherent cation exchange capacity. Most clays contain significant amounts
of iron, magnesium, calcium, potassium and sodium.

There are a several different clay minerals and a very large variation in
the properties of materials called "clay"

Roger Miller