| Sumario: | Glauconite and celadonite coexist at the nanometre scale in Early Jurassic\nsubmarine volcanic rocks of the Betic Cordillera (southern Spain) as a\nresult of microbial activity. Samples from the limit between the two micas, \nrecognizable in scanning electron microscopy, have been extracted using the\nfocussed ion beam technique and studied by high-resolution analytical\nelectron microscopy. Both micas are present as randomly oriented\ndifferentiated small crystals in the boundary area. They define clearly\ndistinct compositional fields with gaps affecting to Fe, Mg and K. At the\nlattice scale, celadonite shows a high degree of order, with homogeneous\norientation of the visible lattice parameters being a difference from\nglauconite, formed by packets no more than 10-layers thick. Smectite layers\nwere also detected alongside glauconite packets, in accordance with X-ray\ndiffractograms which indicate that glauconite is a mica-smectite\ninterstratification being more than 90\u2009% mica layers. The compositional\ngap indicates that celadonite is not the endmember of the glauconitic series\nand the two micas represent two different structural tendencies of mica, \nwith glauconite having more distorted octahedral sheets, indicated by\nsystematically higher b parameters than celadonite.
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