As very little detailed X-ray diffraction investigations have been carried out in South Africa on 2:1 phyllosi1icates in soils,
the aim of the present study was to contribute to the knowledge
of soil genesis, as well as K-fixation and swelling, by investigation
of the clay fraction of selected soils known to be rich
in these minerals. X-ray diffraction analysis has been used
almost exclusively as the investigative technique.
In Chapter 1 a literature review is presented on the reasons
for X-ray diffraction peak broadening and the problems encountered
in the identification of swelling clay minerals. For interstratifications,
the concept of an ABAB layer sequence, considered
as having
suggested
an abab
that the
inter1ayer space,
X-ray diffraction
is questioned.
data from which
It is
the ABAB
arrangement is inferred can as well be explained in terms of
an alternative AAAB layer sequence, having an aabb interlayer
arrangement.
Chapters 2, 3 and 4 deal with layer silicate formation/alteration
in the course of soil development in dolerite and shale-derived
profiles. Dolerite-derived pedons could· be characterized by
one of the following layer silicate suites :
suite i : discrete smectite (Fe-containing beidellite-montmorillonite)
with or without traces of kaolinite and
talc (Vertisol)
suite ii : smectite-kaolinite interstratification (Vertisol)
suite iii : 14 ft minerals (vermiculite, beidellite, montmorillonite,
chlorite) and 7 ft minerals (halloysite, kaolinite )
in about equal proportions (Vertisol and Mollisol)
suite iv : kaolinite with subordinate chlorite and traces of talc
(Oxisol, Ultisol). Eccashale-derived Vertisols are dominated by mica-smectite interstratifications.
The occurrence of an iron-rich pedogenic talc is discussed in
Chapter 4. X-ray and chemical data suggest 30 - 50 mole percent
substitutions of iron for magnesium.
The mineralogical basis for K-fixation has been established in
Chapter 5. Two K-fixing components could be identified :
dioctahedral high-charge vermiculite as a discrete mineral and
random mica-smectite interstratifications with 20 - 60% mica.
In Chapter 6, some of the most expansive soils in South Africa
have been investigated. They can be subdivided into two groups
denoted by the swelling component as follows :
(a) smectite-dominated (the smectite species involved being
most probably beidellite with a heterogeneous charge distribution);
(b) mica-smectite interstratification with random or ordered
stacking arrangement. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1986.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/9624 |
| Date | January 1986 |
| Creators | Buhmann, Christl. |
| Contributors | Fey, Martin Venn. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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