Abstract
An end-member natroalunite of composition (K0.04Na0.96)(Al2.98Fe0.02)(SO4)2(OH)6 occurs in saprolitic clays in a laterite profile developed over Deccan Trap basalts at Matanumad in the Kutch region of Gujarath state, India. Pseudocubic natroalunite crystals, ranging from 0.5 to 1 µm in size, have replaced pseudohexagonal, 2-µm-size platelets of kaolinite. The reverse reaction (kaolinization of natroalunite) has also been observed in the laterites and bauxites immediately adjacent to the saprolite. The kaolinite crystallites that replaced natroalunite occur as a mosaic of anhedral platelets that range in size from 0.1 to 0.3 µm. The formation of natroalunite at Matanumad postdates the laterization of the basalts. It is related to the post-diagenetic formation of sulfuric acid-rich solutions by the oxidation of pyrite in the Eocene-Oligocene black shales of the Matanumad basin. The kaolinitic clays at the top of the saprolite zone have been intensely altered by the acidic solutions, leading to a high concentration of natroalunite.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Biswas, S. K. (1971) Note on the geology of Kutch: Quart. J. Geol. Mining and Metallurgical Soc. India 43, 223–235.
Brophy, G. P., Scott, E. S., and Snellgrove, R. A. (1962) Sulfate Studies II. Solid solution between alunite and jarosite: Amer. Mineral. 47, 112–126.
Cunningham, C. G., Jr. and Hall, R. B. (1976) Field and laboratory tests for the detection of alunite and determination of atomic percent potassium: Econ. Geol. 71, 1596–1598.
Das Gupta, S. K. (1984) Bauxite and aluminum ore resources in India: in Bauxite, L. Jacob, Jr., ed., American Institute of Mining, Metallurgical and Petroleum Engineers, Inc., New York, 451–485 pp.
Hemley, J. J., Hostetler, P. B., Gude, A. J., and Mountjoy, W. T. (1969) Some stability relations of alunite: Econ. Geol. 64, 599–613.
Lindsay, W. L. (1979) Chemical Equilibria in Soils: Wiley, New York, 449 pp.
Menchetti, S. and Sabelli, C. (1976) Crystal chemistry of the alunite series: Crystal structure refinement of alunite and synthetic jarosite: Neues Jahrb. Mineral. Monatshefte H9, 406–417.
Moss, A.A. (1958) Alumian and natroal unite: Mineral Mag. 31, 884–885.
Okada, K., Hirabayashi, J., and Ossaka, J. (1982) Crystal structure of natroalunite and crystal chemistry of the alunite group: Neues Jahrb. Mineral. Monatshefte H12, 534–540.
Ossaka, J., Hirabayashi, J., Okada, K., and Kobayashi, R. (1982) Crystal structure of minamiite, a new mineral of the alunite group: Amer. Mineral. 67, 114–119.
Parker, R. L. (1962) Isomorphous substitution in natural and synthetic alunite: Amer. Mineral. 47, 127–136.
Raymahashay, B. C. (1968) A geochemical study of rock alteration by hot springs in the Paint Pot Hill area, Yellowstone Park: Geochim. Cosmochim. Acta 32, 499–522.
Schoen, R., White, D. E., and Hemley, J. J. (1974) Argillization by descending acid at Steamboat Springs, Nevada: Clays & Clay Minerals 22, 1–22.
Shukla, R. T., Balasubramaniam, K. S., and Madhukara, N. (1983) Paleoenvironment, stratigraphy and genesis of bauxite deposits of Gujarat state, India: in Proceedings of the 2nd International Seminar on Lateritisation Processes, A. J. Melfi and A. Carvalho, eds., I.A.G.C., São, Paulo, Brazil, 209–224.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Chitale, D.V., Güven, N. Natroalunite in a Laterite Profile Over Deccan Trap Basalts at Matanumad, Kutch, India. Clays Clay Miner. 35, 196–202 (1987). https://doi.org/10.1346/CCMN.1987.0350305
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1346/CCMN.1987.0350305