|Abstract or Summary
- A study was conducted to investigate the nature of hydroxy
interlayers in the chlorite-like intergrade clays of three Oregon
soils with respect to kind, amount, stability, and conditions of
The clays of the Hembre, Wren, and Lookout soils, selected to
represent weathering products originating from basaltic materials
under humid, subhumid, and semi-arid climatic conditions respectively,
were subjected to a series of progressive treatments designed to
effect a differential dissolution of the materials intimately associated
with them. The treatments, chosen to represent a range of
increasing severity of dissolution, were (1) distilled water plus
mechanical stirring, (2) boiling 2% sodium carbonate, (3) buffered
sodium citrate-dithionite, (4) boiling sodium hydroxide, and (5)
preheating to 400 °C for 4 hours plus boiling sodium hydroxide.
Extracts from the various steps of the dissolution procedure
were chemically analyzed in order to identify the materials removed
from the clays. X-ray diffraction analysis and cation exchange capacity determinations were made on the clays after each step, and
any differences noted in the measured values were attributed to the
removal of hydroxy interlayers from the clays.
Hydroxy interlayers were found to occur more in the Hembre and
Wren soils than in the Lookout soil, with the most stable interlayers
occurring in the Wren. Soil reaction was one of the major differences
between these soils. The pH values of the Hembre and Wren ranged
between 4.5 and 5.0, while that of the Lookout soil was near neutral
at the surface and 8.3 in the zone of calcium carbonate accumulation.
It appeared from the data, that the parent material of the Wren soil
had reached a more advanced stage of weathering than that of the other
The data from the Hembre clays showed that hydroxy interlayers
formed to the greatest extent in the surface horizon and decreased
with depth. Such interlayers occurred in the A and B horizons of the
Wren clays in about equal amounts, but less in the C horizon. The
zone of clay enrichment in the B horizon of the Wren soil suggests a
downward movement of clay in the profile. Consequently, it is
conceivable that some of the interlayer hydroxides formed in the A
horizon would ultimately have reached the B horizon. There appeared
to be as much interlayering in the C horizon clays of the Lookout
soil as in the upper horizons. This seems to contradict the idea
that interlayering develops most in the upper horizons where weathering
is greatest. The apparent anomaly is resolved, however, if the
lithologic discontinuity in the profile is taken into consideration.
Evidence indicates that the present C horizon of the Lookout soil
may have been a surface soil at one time.
Chemical analysis of the treatment extracts suggests that iron
and magnesium as well as aluminum probably occupy the interlayer
positions of the clays studied. A part of the magnesium was presumed
to have been residuum from brucite interlayers of degraded
The results indicated that intergrade clays may have formed both
from chloritization, and from chlorite degradation. The high amount
of chlorite in the Hembre parent materials together with the acid
environmental conditions probably led to some chlorite breakdown.
Somewhat similar conditions existed in the Wren soil. There is,
however, a high amount of biotite in the parent materials of the
Wren soil that could readily weather to an intergrade by being
altered to smectite or vermiculite and undergoing subsequent
chloritization. The intergrades in the Lookout soil clays apparently
formed from chloritization of smectites in as much as no chlorite was
observed in the parent materials.