Istituto di Geoscienze e Georisorse     
Leoni L., Lezzerini M., Battaglia S., Cavalcante F. Corrensite and chlorite-rich Chl-S mixed layers in sandstones from the 'Macigno' Formation (northwestern Tuscany, Italy). In: Clay Minerals, vol. 45 (1) pp. 87 - 106. The Mineralogical Society of Great Britain and Ireland, 2010.
Corrensite and chlorite-rich chlorite-smectite (Chl-S) mixed-layers occurring in the Macigno Formation of northwestern Tuscany were investigated by XRPD/SEM techniques. The samples from the Macigno outcrops were affected by metamorphism corresponding to the high-diagenesis/low-anchizone transition boundary. The basal spacing of corrensite measured from 00l reflections on EG-Mg2+-saturated samples ranges from 30.97 to 31.18 with a coefficient of variation (CV) of 0.46-0.77%, consistent with the rational pattern of a 1:1 Chl-S periodic stacking sequence. X-ray patterns of heated K+-saturated specimens reveal the presence of two types of corrensite, probably with different interlayer charges on their respective smectite-like layers. The chlorite-rich Chl-S mixed layers coexisting with corrensite consist of R2 chlorite (0.70-0.75)/S and chlorite (0.90)/S with long-range ordering R ≥ 1. SEM observations show that corrensite and chlorite-rich Chl-S mixed-layers are closely mixed on a sub-micron scale. Some grains of corrensite and chlorite-rich Chl-S mixed-layers include zones (2-10 μm) of chlorite composition, as shown by microprobe analyses.
URL: http://claymin.geoscienceworld.org/
Subject corrensite
chlorite-rich Chl-S mixed-layers
Macigno formation
high-diagenesis-low anchizone

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