The heat capacity of two natural chlorite group minerals derived from differential scanning calorimetry

The heat capacity of natural chamosite (X_Fe=0.889) and clinochlore (X_Fe=0.116) were measured by differential scanning calorimetry (DSC). The samples were characterised by X-ray diffraction, microprobe analysis and Mössbauer spectroscopy. DSC measurements between 143 and 623?K were made following the procedure of Bosenick et?al. (1996). The fitted data for natural chamosite (CA) in J?mol^?1?K^?1 give: C _p,CA = 1224.3–10.685?×?10³?×?T ^??0.5???6.4389?× 10⁶?×T ^??2?+?8.0279?×?10⁸?×?T ^??3 and for the natural clinochlore (CE): C _p,CE = 1200.5–10.908?×?10³?×T ^??0.5?? 5.6941?×?10⁶?×?T ^??2?+?7.1166?×?10⁸?×?T ^??3. The corrected C _p-polynomial for pure end-member chamosite (Fe₅Al)[Si₃AlO₁₀](OH)₈ is C _p,CAcor = 1248.3–11.116?× 10³?×?T ^??0.5???5.1623?×?10⁶?×?T ^??2?+?7.1867?×?10⁸×T ^??3 and the corrected C _p-polynomial for pure end-member clinochlore (Mg₅Al)[Si₃AlO₁₀](OH)₈ is C _p,CEcor = 1191.3–10.665?×?10³?×?T ^??0.5???6.5136?×?10⁶?×?T ^??2?+ 7.7206?×?10⁸?×?T ^??3. The corrected C _p-polynomial for clinochlore is in excellent agreement with that in the internally consistent data sets of Berman (1988) and Holland and Powell (1998). The derived C _p-polynomial for chamosite (C _p,CAcor) leads to a 4.4% higher heat capacity, at 300?K, compared to that estimated by Holland and Powell (1998) based on a summation method. The corrected C _p-polynomial (C _p,CAcor) is, however, in excellent agreement with the computed C _p-polynomial given by Saccocia and Seyfried (1993), thus supporting the reliability of Berman and Brown's (1985) estimation method of heat capacities.