Dickite, Nacrite and Possible Dickite/Nacrite Mixed-Layers from the Betic Cordilleras (Spain)

M. D. Ruiz Cruz
Departamento de Química Inorgánica, Cristalografía y Mineralogía. Facultad de Ciencias. Universidad de Málaga (Spain)

Abstract: Nacrite, dickite and intermediate dickite-nacrite phases have been identified from the upper Paleozoic sequences of the Malúguide Complex (Betic Cordilleras, Spain). Nacrite developed as euhedral, pseudohexagonal or elongated crystals within sandstones and thin, irregular veins. Dickite developed preferently within extensive zones of fractures as very irregular, compact packets. Intermediate phases occurred in the sandstones and veins similar to the nacrite, or accompanying dickite. The mineral assemblage of the sandstones includes quartz-muscovite-kaolinite-type minerals, with or without albite, carbonates, chlorite and mixed-layers containing chlorite. The metamorphic conditions in which these minerals formed belong to anchizone, as can be deduced from the IC values. Dickite, nacrite and intermediate phases were studied by X-ray diffraction, infrared spectroscopy, differential thermal analysis and microscopy. The results for dickite indicate a well-ordered mineral and agree with most of the published data. Conversely, IR spectra and DTA curves of nacrite show some differences in relation to the available data for this mineral. Based on the comparison with dickite and nacrite data, intermediate phases can be interpreted either as disordered varieties or as mixed-layered dickite/nacrite.

Key Words: Dickite • Differential thermal analysis • Infrared spectroscopy • Mixed-layers • Nacrite • Very low-grade metamorphism • X-ray powder diffraction

Clays and Clay Minerals; June 1996 v. 44; no. 3; p. 357-369; DOI: 10.1346/CCMN.1996.0440305
© 1996, The Clay Minerals Society
Clay Minerals Society (www.clays.org)