A Study of a Deep Weathering Profile on Granite in Peninsular Malaysia: II. Mineralogy of the Clay, Silt, and Sand Fractions

103

Abstract--Parallel-oriented and exceptionally long (> 10 #m) tubes of halloysite occur in the pallid zone of a deeply-weathered lateritic profile on granite in southwest Australia.Transmission electron microscopy and selected-area electron diffraction of ultrathin sections showed that kaolinite plates within pseudomorphs of mica crystals had fractured at irregular intervals along the a crystallographic axis to produce laths elongated along the b axis. The laths near the edges of the pseudomorphs were less constrained by the pseudomorph and had roiled to produce halloysite tubes. The tubes varied in diameter and degree of roundness. Some tubes were polyhedral rather than cylindrical in cross section. The length and number of planar faces in a tube and the angle between faces varied, exhibiting no consistent pattern.Tubes in dispersed clay samples showed two types of twinning. In the first type, tubes and associated laths were joined together side by side. In the second type, single tubes bifurcated into two individual tubes. It is proposed that the first type of twinning occurred by folding of adjacent laths that remained joined together while the second type occurred due to exfoliation of a thick lath followed by folding of the exfoliated lath fragments into tubes.Analytical electron microscopy showed that the chemical compositions of halloysite tubes, laths, and kaolinite plates were similar with the average cation exchange capacity of single tubes being small (4.5 meq/100 g) but higher than values for laths (2.8 meq/100 g) and plates (1.9 meq/100 g).

Section: Morphologymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

An Electron Optical Investigation of the Alteration of Kaolinite to Halloysite

Singh¹,

Gilkes

1992

103

“…Topotactic or epitactic alteration of mica or feldspar to halloysite has not previously been identified in nature (Gilkes et aL, 1986;Singh and Gilkes, 1992), whereas kaolinite formed from mica by topotactic alteration can subsequently produce halloysite tubes . Nevertheless, halloysite may also be formed through alteration of feldspar via solution or a non-crystalline intermediate stage (Eswaran and Bin, 1978;Singh and Gilkes, 1992). Robertson and Eggleton (1991) explained the transformation of platy kaolinite into spiral halloysite rods by a loss of structural rigidity at points along the kaolinite crystal due to hydration of kaolinite.…”

Section: Introductionmentioning

confidence: 99%

Kaolinite to Halloysite-7 Å Transformation in the Kaolin Deposit of São Vicente De Pereira, Portugal

Boboş

Duplay²,

Rocha

et al. 2001

Abstract~he transformation of kaolinite to halloysite-7 .~ was identified in the kaolin deposit of S~o Vicente de Pereira (SVP), using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). Both the 02,1 i and 13,13 reflections show changes in the XRD patterns along the kaolinite to halloysite-7 ,~ transition, and the FTIR spectra show changes corresponding to both OH and Si-O-stretching bands and Al-O-Si-bending vibrations. The interlayer water content in the kaolinite structure increases during transition. The two-layer periodicity of well-ordered kaolinite and rolling up of kaolinite plates are observed using hi~h-resolution transmission electron microscopy (HRTEM). Long and short tubes exhibit halloysite-7 A. No structural Fe was found in the kaolinite samples. Analytical electron microscopy (AEM) indicates no substitution of AP § for Si 4+. The Si/A1 ratio shows values of --1 for the kaolinite and rolled kaolinite plates. The 27A1 magic angle spinning neutron magnetic resonance (MAS-NMR) spectra display a resonance centered at -1 ppm, assigned to six-coordinated aluminum. The transformation of kaolinite to halloysite-7 A. is controlled by surface reaction.

“…Several studies have found a decrease in the abundance ofhalloysite relative to that of kaolinite with an increase in degree of weathering of softs or with increasing proximity to the surface of soil profiles (Shimuzu, 1972;Eswaran and Wong, 1978;Calvert et al, 1980;Hughes, 1980;Hewitt and Churchman, 1982), Hence, it is tempting to infer that halloysite transforms to kaolinite with weathering. The apparently continuous series of X-ray powder diffraction (XRD) patterns of Ross and Kerr (1934) and Brindley and Robinson (1946) showing increasing order from halloysite to highly crystalline kaolinite also suggest a natural progression between halloysite and kaolinite.…”

Section: Introductionmentioning

confidence: 99%

Relevance of Different Intercalation Tests for Distinguishing Halloysite from Kaolinite in Soils

Churchman¹

1990

--The expandabilities of kaolin-group minerals in different horizons in 10 soils from New Zealand and Fiji were measured immediately after the application offormamide and after the sequential application of hydrazine, water, and glycerol (HWG treatment). The expandabilities of these minerals in some of the soil samples with dimethylsulphoxide (DMSO) and after long-term (4-day) formamide treatments were also measured. The abundance of characteristic halloysite shapes was determined from electron micrographs of selected samples. The cxpandabilities of several non-soil kaolinite samples with the DMSO and HWG treatments were also measured.The expansion of kaolin-group minerals showed the same trends within almost all profiles, whether determined using formamide (by the immediate-formamide treatment) or glycerol (by the HWG treatment). Except where both treatments led to complete intercalation, the HWG treatment always caused more expansion of kaolin-group minerals than obtained immediately after formamide application. The HWG treatment expanded some non-soil kaolinite samples, but well-crystallized kaolinite was not affected by this treatment. The DMSO treatment expanded kaolin-group minerals in the soils to a similar extent as the HWG treatment and also expanded well-crystallized kaolinite. The degree of expansion resulting from the immediate-formamide treatment matched abundance of typical halloysite particle shapes more closely than the degree of expansion given by the other intercalation treatments. The degree of expansion immediately following formamide application could be diminished, if the samples were heated at 40 _+ 5~