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Using
laterite
by
Robert Paul Hudson
What is laterite?
Laterite is a soil
or rock found in the tropics that is very high in iron. It is not
considered clay because it is usually absent of silica, and is instead a
mixture of fine grains of quartz with minute scales of hydrates of
alumina. Laterite is a pedogenic and highly weathered natural material
formed by the concentration of hydrated oxides of iron and aluminium.
Acids cause the alumina and iron to leave the silica as a residue in the
form of quartz.
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I found this information on the internet:
In order for laterite to form the following
conditions must occur:
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There should be parent rock rich in iron
and aluminium and silica. (When laterite
is formed, the silca is removed)
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The climatic conditions should include
moderate to high temperatures and
moderate to high rainfall with distinct
dry and wet season.
Laterite occurs mostly in the tropical and
sub-tropical regions with lowest maximum
temperatures above 18șC and the average
temperature over 24șC. |
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Theoretical conditions for
concretionary laterite development
|
Annual rainfall (mm) |
750 - 1000 |
1000 - 1500 |
1500 - 2000 |
|
Thornthwaite Moisture Index |
-40 to -20 |
-20 to 0 |
0 to 30 |
|
Length of Dry Season |
7 |
6 |
5 |
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Type of Laterite |
Rock laterite |
Hard concretionary gravels |
Min. requirements for
concretions to develop |
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I got into an argument a few years ago with Roger Miller who
claimed there was laterite in North America. Below is a graph
from the internet showing all known ancient deposits of laterite.
Notice there is none in North America! |
Classifications of laterite
|
Age |
Recommended Name |
Characteristics |
Equivalent terms in literature |
|
Imature
(young) |
PLINTHITE |
Soil fabric containing a significant amount of laterite
material.
Hydrated oxides at the expense of some soil material.
Unhardened nodules present, but may be slight evidence of
concretionary development |
Plinthite,
laterite, lateritic clay |
|
|
NODULAR LATERITE |
Distinct hard concretionary nodules present as separate
particles |
Laterit gravel, ironstone gravel, pisolitic gravel |
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HONEYCOMB LATERITE |
Concretions have coalesced to form a porous structure which may
be filled with soil material. |
Vesicula laterite, pisolitic ironstone, cellular ironstone,
spaced pisolitic laterite |
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HARDPAN LATERITE |
Indurated laterite layer, massive and tough. |
Ferricrete, ironstone, laterite crust, vermiform laterite,
packed pisolitic laterite |
|
Mature
(old)
|
SECONDARY LATERITE |
May be nodular honeycomb or hardpan, but is result of erosion of
pre-existing layer and may display brecciated appearance. |
Use in the aquarium
I believe the German company Dupla was the first to
market laterite for the aquarium. Since it is found in the same tropical
regions as the plants we use come from, and laterite run off is found in
the waters of the tropics, it seems a logical conclusion that laterite
is part of tropical plants natural element. The high concentration of
iron provides an unlimited source of the mineral for the plants, it is
however void of any other minerals and contains no organic material as a
source of nitrogen. The oxidized iron (Fe3) can be turned into Fe2, (the
form of iron most easily used by plants) by organic acids in the
aquarium. This happens naturally as the aquarium ages, but can be sped
up by adding a small amount of peat to the laterite. It is also believed
that the soft texture of the lateric soil is conducive to plant root
hairs and may be able to absorb other nutrients from the water.
To use laterite, you mix a small amount with gravel or
course sand and add peat if desired, to the bottom layer of the
substrate and then cover it with at least two inches of a top layer of
gravel or sand. Using laterite instead of a clay gravel enables you to
use any type of decorative gravel you choose. It also does not affect
the pH or add silica to the water. Many people have sworn that they get
tremendous growth with plants such as Echinodorus and Cryptocorynes. It
was the use of laterite that prompted the introduction of clay gravels
such as Seachem's Flourite, Eco Complete, and others. The premise of
using either clay or laterite is that plants need a source of iron in
the substrate.
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