The Role of Dehydration in the Development of Laterite^ 
G. Donald Sherman, Yoshinori 
Kanehiro, and Yoshito Matsusaka^ 
Soil formation in tropical regions is deter- 
mined by the nature and extent of the chemi- 
cal weathering of the soil- forming materials. 
The intense chemical weathering and the va- 
rying length of time of exposure of minerals 
to weathering have resulted in the develop- 
ment of a broad sequence of soil formation 
in the tropical areas of the world. Sherman 
(1949) has shown that the soils of the Ha- 
waiian Islands exhibit a sequence of soil de- 
velopment which can be related to a sequence 
of mineral weathering as proposed by Jackson 
et aL (1948). This sequence of soil formation 
represents a series of successive stages of sec- 
ondary mineral development with the follow- 
ing order of soils rich in: ( 1 ) primary minerals; 
(2) montmorillonite; (3) kaolinite; (4) hy- 
drated sesquioxides; and (5) dehydrated ses- 
quioxides. The end product of this weathering 
cycle would be either a ferruginous laterite or 
a bauxite laterite, depending on the environ- 
mental conditions. These two products rep- 
resent two extremes of a wide range of weath- 
ered end-products, as the intermediate member 
— a ferruginous bauxitic laterite — is quite 
common (Harrison, 1934). 
Ferruginous laterite was described by Bu- 
chanan (1807). As described by Buchanan, 
laterite is a soil horizon which has a very high 
content of iron oxides. These iron oxides 
exist as the minerals, limonite, goethite, hema- 
1 Published with the approval of the Director of the 
Hawaii Agricultural Experiment Station, Honolulu, 
Hawaii, as Technical Paper 273. Manuscript received 
December 2, 1952. 
2 Chairman and Junior Chemists, respectively. De- 
partment of Soils and Agricultural Chemistry, Hawaii 
Agricultural Experiment Station. 
tite, and magnetite. The profile of the fer- 
ruginous laterite must have a horizon rich in 
iron oxide which will harden, on exposure, to 
an indurate layer with brick-like properties. 
The ferruginous ' horizon may contain con- 
cretions of iron oxide in which case it is a 
pisolithic laterite, or the iron oxide may exist 
as a lens in a porous matrix which is known 
as a vesicular laterite, according to Pendleton 
(1941). Ferruginous laterite may also develop 
as a massive horizon near or at the surface 
which on exposure will harden and develop 
a uniform, structureless crust, or corapace. 
Soils of this type have been described by 
Aubreville (1947, 1948), Chevalier (1948), 
and Sherman (1950). 
The mode of origin, or formation, of fer- 
ruginous laterite has been a point of contro- 
versy. Glinka (1927) believed that laterites 
formed under both evergreen and savannah 
types of vegetation. Richthofen's views (I860) 
differed from Glinka's in that he postulated 
the formation of laterite under a former forest 
vegetation which had been succeeded by a 
shrub and grass vegetation. In other words, 
as soils degraded they could not support the 
evergreen forest; thus, the forest disappeared^, 
and was replaced by a lower level of vegeta- 
tion. Harrassovitz (1930), Holmes (1914), 
and Campbell (1917) concluded from their 
studies that laterite formed only where cli- 
matic conditions were conducive to the up- 
ward movement of the dissolved soil sesqui- 
oxides, which would only occur under alter- 
nating wet and dry conditions. On the other 
hand, Pendleton (1941, 1942, 1946) believes 
that laterites are formed by the oxidation and 
438 
