Mixed-layer chlorite/smectite (corrensite) in ophiolitic rock alteration products

Corrensite from the Tare Valley (Northern Apennine, Italy) was examined with X-ray powder diffraction (XRD) and high resolution transmission electron microscopy (TEM). XRD showed that the mineral is a well ordered corrensite, i.e. with regular 1:1 chlorite/smectite stacking. The TEM study (selected area diffraction patterns and lattice-fringe images) showed that the predominant types of stacking belong to collapsed di- or trioctahedral smectite-like minerals and to chlorite. The arrangement of alternating chlorite and collapsed smectite layers (14+10 Angstrom), which is typical of corrensite, is uncommon.