Diagenetic Kaolinite/Dickite (Betic Cordilleras, Spain)

M. D. Ruiz Cruz and L. Moreno Real
Departamento de Química Inorgánica, Cristalografía y Mineralogía, Facultad de Ciencias, 29071, Málaga, Spain

Abstract: The lower Permo-Triassic sediments of the Maláguide Complex contain abundant dickite. Whole rocks were studied by optical microscopy, scanning electron microscopy, and X-ray powder diffraction. The 2–20 µm and < 2 µm size fractions were extracted and analyzed by scanning and transmission electron microscopy, X-ray powder diffraction, infrared spectroscopy, differential thermal analysis, and thermogravimetry.

In the coarse-grained samples, the 2–20 µm size fraction consisted of well-crystallized dickite associated with minor quantities of kaolinite, illite, quartz, and hematite. XRD patterns of the fine-grained samples and the <2 µm fractions showed the existence of well-crystallized minerals in which several reflections of dickite (11l, 02l) were absent and the 132/13 2 ¯ reflections were shifted. These patterns suggest the presence of an intermediate member between well-crystallized dickite and well-crystallized kaolinite. Only locally high-order reflections are present at 10.5 Å and 18–22 Å. DTA and IR data agree with those from XRD.

The observed compositional and structural variations are a function of the lithology and the particle size of the sample. The sequence kaolinite → kaolinite/dickite → dickite is proposed for the development of these materials during Alpine metamorphism.

Key Words: Crystallinity • Dickite • Differential thermal analysis • Electron microscopy • Infrared spectroscopy • Interstratified minerals • Kaolinite • Thermogravimetry • X-ray powder diffraction

Clays and Clay Minerals; October 1993 v. 41; no. 5; p. 570-579; DOI: 10.1346/CCMN.1993.0410507
© 1993, The Clay Minerals Society
Clay Minerals Society (www.clays.org)