Low- and high-temperature heat capacities of natural ferrocarpholite and magnesiocarpholite samples from the island of Crete (Greece) were measured using the heat-capacity option of the Physical Properties Measurement System (PPMS, Quantum Design), which is based on the principles of heat-pulse calorimetry (HPC), and by differential scanning calorimetry (DSC). Comprehensive chemical analyses also have been performed on these samples by electron-microprobe analysis (EMPA), inductively coupled plasma mass spectrometry (ICP-MS), and Karl-Fischer titration (KFT) for H2O. In addition, the ferrocarpholite sample has been investigated by Mössbauer spectroscopy (MS). The measured heat capacities were corrected to end-member compositions of ferrocarpholite and magnesiocarpholite. The standard entropy of end-member ferrocarpholite Fe2+Al2[Si2O6](OH)4 and end-member magnesiocarpholite MgAl2[Si2O6](OH)4 were determined as 248.1 ± 0.3 J/(mol·K) and 221.5 ± 0.2 J/(mol·K), respectively. The CP-polynomial for end-member ferrocarpholite is CP = 652.05 − 6.0995 × 103T−0.5 − 2.0980 × 106T−2 + 2.9396 × 108T−3 [J/(mol·K)], valid in the temperature range of 298.15–625 K, and that for end-member magnesiocarpholite is CP = 644.08 − 6.0921 × 103T−0.5 − 2.2825 × 106T−2 + 3.3182 × 108T−3 [J/(mol·K)], valid in the temperature range of 298.15–725 K.

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