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Scanning Electron Microscope Morphology of Deeply Weathered Granite

Published online by Cambridge University Press:  01 July 2024

R. J. Gilkes ,
Anchalee Suddhiprakarn  and
T. M. Armitage
R. J. Gilkes
Affiliation:
Department of Soil Science and Plant Nutrition, University of Western Australia, Nedlands, Western Australia, 6009
Anchalee Suddhiprakarn*
Affiliation:
Department of Soil Science and Plant Nutrition, University of Western Australia, Nedlands, Western Australia, 6009
T. M. Armitage
Affiliation:
Department of Soil Science and Plant Nutrition, University of Western Australia, Nedlands, Western Australia, 6009
*
1Permanent address: Department of Soils, Kasetsart University, Bangkok, Thailand
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Abstract

Laterite profiles developed from granite in southwestern Australia were studied by scanning electron microscopy. The morphology of soil materials reflects the mineralogy of secondary minerals formed from feldspar. In the saprolite, etched feldspar surfaces are coated with kaolinite or radiating, spherical aggregates of tubular halloysite. In the lower pallid zone these minerals have replaced most of the feldspar. In the upper pallid zone a porous framework has developed consisting mainly of quartz and gibbsite with 5-/μm euhedral gibbsite crystals in voids. Halloysite crystals in the upper pallid zone are partly unrolled and have splayed ends. Differences in mineralogy and morphology between profiles are thought to be due to variations in the intensity of leaching.

Резюме

Резюме

С помощью электронного сканирующего микроскопа изучались латеритные разрезы, развившиеся в результате выветривания гранита в юго-западной Австралии. Морфология почвенных материалов отражает минералогию вторичных минералов, образованных из полевого шпата. В сапролите, выветрелые поверхности полевого шпата покрыты каолинитом или лучевыми, сферическими агрегатами трубчатого галлуазита. В нижней, паллидной зоне эти минералы почти полностью заместили полевой шпат. В верхней паллидной зоне образовалась пористая структура, состоящая в основном из кварца и гиббсита с 5 μм идиоморфными кристаллами гиббсита в полостях. Галлуазитовые кристаллы в верхних паллидных зонах частично развернуты и имеют скошенные концы. Различия в минералогии и морфологии разрезов объясняется изменением интенсивности выщелачивания. [N. R.]

Resümee

Resümee

Lateritprofile, die sich im südwestlichen Australien im Granit gebildet haben, wurden mittels Rasterelektronenmikroskopie untersucht. Die Morphologie des Bodenmaterials zeigt die Mineralogie der Sekundärminerale, die sich aus Feldspat gebildet haben. Im Rückstandsgestein sind geätzte Feldspatoberflächen mit Kaolinit oder radial strahligen Aggregaten aus röhrenförmigem Halloysit überzogen. In der tieferen bleichen Zone haben diese Minerale fast den ganzen Feldspat ersetzt. In der oberen bleichen Zone hat sich ein poröses Gerüst gebildet, das hauptsächlich aus Quarz und Gibbsit besteht, mit 5 μm großen idiomorphen Gibbsitkristallen in den Hohlräumen. Die Halloysitkristalle in der oberen bleichen Zone sind teilweise entrollt und haben nach außen gebogene Enden. Die Unterschiede in der Mineralogie und Morphologie der einzelnen Profile werden auf eine verschieden starke Auslaugung zurückgeführt. [U. W.]

Résumé

Résumé

Des proflies de latérite développés à partir de granite en Australie du sud ouest ont été étudiés par microscopie électronique balayante. La morphologie des matériaux du sol réflète la minéralogie des minéraux secondaires formés à partir de feldspar. Dans la saprolite, des surfaces de feldspar gravées sont recouvertes de kaolinite ou d'aggrégats sphériques et branchants d'halloysite tabulaire. Dans la zone inférieure pâle, ces minéraux ont remplacé la plupart des feldspars. Dans la zone pâle supérieure, une charpente poreuse s'est développée consistant surtout de quartz et de gibbsite avec des cristaux euhédraux de 5μm de gibbsite dans les vides. Les cristaux d'halloysite dans la zone pâle supérieure sont partiellement déroulés et ont des bouts ébrasés. On croit que les différences de minéralogie et de morphologie entre les profiles sont dues à des variations dans l'intensité du lessivage. [D. J.]

Keywords

FeldsparGibbsiteGraniteHalloysiteKaoliniteScanning electron microscopyWeathering
Type
Research Article
Information
Clays and Clay Minerals , Volume 28 , Issue 1 , February 1980 , pp. 29 - 34
Copyright
Copyright © Clay Minerals Society 1980

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