Original paper

New data for metamorphic vermiculite

Cruz, Maria Dolores Ruiz

European Journal of Mineralogy Volume 11 Number 3 (1999), p. 533 - 548

31 references

published: May 25, 1999
manuscript accepted: Dec 22, 1998
manuscript received: Sep 15, 1997

DOI: 10.1127/ejm/11/3/0533

BibTeX file

ArtNo. ESP147051103012, Price: 29.00 €

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Abstract Vermiculite-like minerals from a very low-grade metamorphic sequence (Maláguide Complex, Betic Cordillera, Spain) were studied by optical microscopy, X-ray diffraction (XRD), differential thermal analysis /thermogravimetry (DTA-TG), electron microprobe (EMPA), and transmission/analytical electron microscopy (TEM/AEM). They occur as transformation products of chlorite, the conversion sequence being: chlorite → chlorite/vermiculite mixed-layers → vermiculite. This sequence is characterized by a continuous chemical evolution that includes Fe+Mg loss and an increase in Si/Al ratio. These chemical changes are accompanied by a variable increase in alkali (K and Na) and Ca. AEM data of homogeneous packets have permitted the chemical characterization of high-temperature or metamorphic vermiculite, which shows a narrow compositional range. This mineral sequence probably developed during the Alpine metamorphic event at less than 400°C, and the phases formed may be considered, in the light of the available data, as intermediate in the chlorite to biotite transformation, their development being probably dependent on both temperature and cation availability


Betic Cordillerabiotitechloritemixed-layer mineralsvermiculiteTEMvery low-grade metamorphismSpain