Serpentine-smectite in interstratified minerals from Lower Silesia (SW Poland)

Interstratified serpentine-smectite was found in the fine-grained fraction of altered metasomatic contact biotite-schists developed between serpentinite and granite-type rocks (Lower Silesia ophiolite sequence, Poland). Ni-rich serpentine-smectite is R0-interstratified lizardite (0.80)-stevensite (0.15)-vermiculite-like (0.05), with a coherent scattering domain (csd) of 5 layers (mean value). The Mg-rich variety of serpentine-smectite is R1 lizardite (0.80)-stevensite (0.20) with a csd size of 7 layers (mean value). A transmission electron microscope study revealed complex layer relationships, with zones composed of various serpentine-smectite packets having lizardite/smectite ratios of 3:1, 2:1, 1:1, 4:1 and scarce serpentine segregations. In both cases, the serpentine-smectites appear to be late products of alteration of the parent biotite-schist. Experimental and calculated positions and intensities of reflections of the ethylene glycol-saturated, heated (250 degrees C, thermal stage), and air-dried samples are in good agreement. Calculated X-ray diffraction patterns for interstratified glycolated and anhydrous serpentine-smectite are included in the Appendix.