Fig. 4From: The pioneer work of Bernard Kübler and Martin Frey in very low-grade metamorphic terranes: paleo-geothermal potential of variation in Kübler-Index/organic matter reflectance correlations. A reviewClay-mineral fraction XRD-runs of air-dried samples calibrated with metamorphic temperatures from fluid inclusions given in °C. Il illite, chl chlorite, sm smectite. Modified after Mullis et al. (2002). The carbonate content and type of phase controls the stability of the smectite (Ca–Mg rich)Back to article page