Sample powders for X-ray diffraction (XRD) and for stable isotope measurements were obtained from surfaces of the polished slabs, using a handheld microdrill. The XRD measurements were performed on a X'PERT PRO diffractometer equipped with a copper anode λ=1.54 Å at 40 mA and 40 kV current. Qualitative and quantitative analyses were carried out applying the Rietveld method using EXPGUI-GSAS (Rietveld, 1969; Larson and von Dreele, 1994; Toby, 2001). The accuracy was estimated±1 wt.-%. The Mg-content in calcite was determined using the method of Titschack et al. (2011).Values in parentheses represent the deviation in units of last digits. Rp, Rwp and χ2 are agreement factors indicative of the goodness of the Rietweld analyses (Toby, 2006)