“…Silica impurity contributions to the measured heat capacities vary between 20% and 27% for MX-80 and 7% and 8% for IMt-2 and are about 0.8% for ISCz-1. For microcline, heat capacity data were taken from Openshaw et al (1976) between 5 and 298 K and from Robie and Hemingway (1995) between 298.15 and 520 K. For kaolinite, data were taken from Robie and Hemingway (1991) between 7 and 298 K and from Robie and Hemingway (1995) between 298.15 and 520 K. For rutile, data were provided by Shomate (1947) between 52 and 298 K and by Robie and Hemingway (1995) between 298.15 and 520 K. For these latter impurities, data were extracted from two different referenced works, which cover, respectively, temperature ranges lower and higher than 298.15 K. For a given impurity (except silica), some differences were observed between heat capacities at 298.15 K. Nevertheless, the resulting errors in the heat capacity of the minerals at 298.15 K are lower than 0.03% for mixed-layer and 0.003% for illite. They are small compared to the expected maximum absolute errors on measurements of the heat capacities of the minerals, which are: 1% between 5 and 30 K; 0.05-0.1% between 30 and 100 K; 0.03% from 100 to 380 K for MX-80 and ISCz-1 and from 100 to 400 K for IMt-2 (adiabatic calorimetry measurements); and 0.1% in the range 380-520 K for MX-80 and ISCz-1 and in the 400-510 K range for IMt-2 (DSC measurements).…”