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A new occurrence of the hydrated aluminium sulphate zaherite, from Pofadder, South Africa

Published online by Cambridge University Press:  05 July 2018

G. J. Beukes ,
A. E. Schoch ,
H. de Bruiyn ,
W. A. Van der Westhuizen  and
L. D. C. Bok
G. J. Beukes
Affiliation:
Department of Geology, University of the Orange Free State, Bloemfontein, South Africa
A. E. Schoch
Affiliation:
Department of Geology, University of the Orange Free State, Bloemfontein, South Africa
H. de Bruiyn
Affiliation:
Department of Geology, University of the Orange Free State, Bloemfontein, South Africa
W. A. Van der Westhuizen
Affiliation:
Department of Geology, University of the Orange Free State, Bloemfontein, South Africa
L. D. C. Bok
Affiliation:
Department of Geology, University of the Orange Free State, Bloemfontein, South Africa
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Abstract

A new occurrence of zaherite is reported from a sillimanite quarry 65 km west of Pofadder, Bushmanland, South Africa. It occurs as earthy white to light bluish-green cryptocrystalline material in narrow veins, in close association with natro-alunite and hotsonite, a new hydrated aluminium phosphate-sulphate. Scanning electron micrographs show an orientated wavy texture and tubular fibres. The optical and physical properties agree with those of the type material described from Pakistan, and it can be added that the mineral is biaxial positive with a moderate 2V and length-fast orientation. The new chemical analysis yields an ideal formula of Al12(SO4)5(OH)26·20H2O, which is identical to that of the type material. The white and light bluishgreen varieties are identical in major element composition but yielded trace Cu values of 1281 and 2408 ppm respectively. The X-ray powder diffraction pattern fits a triclinic symmetry (a 5.55, b 9.74, c 18.43Å, α 99.71°, β 89.13° γ 94.97°), and is dominated by one intense reflection at 18.12 Å, representing 001. The most important of the weak lines are (d, I, hkl): 9.56, 5, 010; 9.08, 4, 002; 4.82, 6, 01; 4.61, 8, 110; 4.56, 4, 02; 4.44, 4, 021; 3.61, 4, 1; 3.22, 8, 015. The differential thermal properties are characterized by endothermic peaks at 190, 470, and 685°C and a duplex at 880 and 910°C The infrared absorption spectrum is characterized by absorption bands centring about 905, 960, 985, 1150, 1700, and 3600 cm−1.

Type
Research Article
Information
Mineralogical Magazine , Volume 48 , Issue 346 , March 1984 , pp. 131 - 135
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1984

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References

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