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Re: Laterite



Christopher Coleman replied to an original post from Robert H, to which
Mr. H now responds...

> Well Chris, I think you need to relax your tone a bit here. I am not
> trying to make headline breaking news here, but to only have a better
> understanding of it myself.

You have a reasonable goal, and Chris's response was a bit terse, but
lot's of us get that way about the upteenth time we deal with the same
topic.

> >> have always thought the term was over used to describe
> >> just about any type of clay.
> > It is not clay.  This is a misnomer.  Laterite is a soil containing
> > a mixture of minerals.  Understanding laterite is possible by
> > understanding what clay is and than realising laterite lacks any of 
the
> > properties.
> There have been numerous refrences to laterite as clay on this list,
> rec.aquaria and many other forums. Laterite does NOT contain a mixture
> of minerals to any extent. Most has been leeched out and laterite is
> formed by weathered basalt.

Are you surprised that many internet forums might be providing you with a
hat full of misinformation?

If you read the archive (I know, its difficult to sort out all the
references to "laterite") you wil find that laterite is a clay only in the
sense that it's "really fine grained stuff" and then only if it has been
ground up really fine.  You will also find that laterite is composed
largely of oxyhydroxides of iron and aluminum - most commonly aluminum.  
It contains a small proportion of other minerals, including the clay
mineral halloysite.  Many rocks and most soils have a higher clay mineral
content than laterite.

The constituents of laterite are minerals.  Laterite is leached of any
mineral that is at all soluble, but the material that's left is still
mineral.  The common minerals have obscure (to the layman) names like
goethite, gibbsite, boehmite and diaspore.

Furthermore, laterite does not form just from basalts.  I don't think that
laterization depends much at all on the parent material. Even the very
restrictive group of economically important laterites (bauxites) form on a
wide range of parent materials.

[snip]

> >>  "If you would like a response from a whole group of clay minerals
> >> scientists
> > Again.  It is not clay.

> Well then maybe you should pose a question to this server of "clay
> mineral scientists", who according to you arent clay mineral scientists.

I don't think Chris was implying that the people on the list aren't clay
mineral scientists.  The point is that laterite contains few clay
minerals, so the clay mineral scientists are the wrong crowd to be talking
with.

> > So can I infer from all your rambling that you think laterite is found 
> > in the USA? Can you tell me where?

By my reference (Lefond, ed. 1975.  "Industrial Minerals and Rocks"),
lateritic (aka bauxitic) material is found in several areas of the US, all
of them "fossil" deposits:  12-23 million year old deposits occur in
Oregon and Washington, 35-55 million year old deposits are found in
Arkansas, Alabama, Georgia and Mississippi and 270-320 million year old
deposits are found in Missouri and Pennsylvania.

If you live in one of those areas and are interested in finding out more
about them you might be able to contact local offices of the US Geological
Survey (Department of Interior), state Geological Surveys or Bureaus of
Mines, or local schools and/or universities with departments of Geology or
soil science.  In all of the U.S. occurences the laterite is likely to be
a rock and not at all clay like.

In addition there are other types of iron deposits that occur all over the
world.  Finely crushed ore from some of these deposits might make a
suitable substitute for laterite.  But as always, YMMV.


Roger Miller