Table 3.

Enthalpy and entropy change due to heating from 0 to 298.15 K for the investigated Fe-containing minerals, i.e., hedenbergite (hed), fayalite (fa), and annite (ann)

	Heat content		Entropy
	Calorimetry	DFT	Calorimetry	DFT
	$\underset{0}{\overset{298.15}{\int }}{C}_{\text{P}}\text{d}T$	$\underset{0}{\overset{298.15}{\int }}{C}_{\text{V}}\text{d}T$	$\underset{0}{\overset{298.15}{\int }}\frac{C_{\text{P}}}{T}\text{d}T$	$\underset{0}{\overset{298.15}{\int }}\frac{C_{\text{V}}}{T}\text{d}T$
	kJ/mol	kJ/mol	J/mol/K	J/mol/K
K2O	13.000	14.232	94.140	94.722
CaO	6.749	6.877	38.212	38.839
FeO	9.136	7.533	60.752	44.718
Al2O3	10.020	10.171	50.950	51.831
SiO2	6.916	7.066	41.463	43.733
H2O	6.388	3.640	41.632	22.182
hed	28.226	27.109	174.2	159.884
fa	22.489	20.165	151.0	118.871
ann	63.955	57.659	411.4	343.954
ΔR-hed	− 1.5	− 1.4	− 7.7	− 11.1
ΔR-fa	− 2.7	− 2.0	− 12.0	− 14.3
ΔR-ann	− 2.1	− 2.0	− 9.4	− 16.9

Δ_R-hed, Δ_R-fa, Δ_R-ann represents the reaction heat content $\left(\underset{0}{\overset{298.15}{\int }}{C}_{\text{P}}\text{d}T\right)$ and reaction entropy $\left(\underset{0}{\overset{298.15}{\int }}\frac{C_{\text{P}}}{T}\text{d}T\right)$ from their oxides, i.e., of the reaction CaO + FeO + 2*SiO₂ = CaFeSi₂O₆ in the case of hedenbergite. The C_P data were taken from the Janaf-tables (Chase 1998) for the oxides, from Haselton et al. (1987) for hedenbergite, from Robie et al. (1982) for fayalite and from Dachs and Benisek (2015) for annite. The C_V data were calculated by the DFT method