The heat capacities, CPo, of magnesio-anthophyllite, diopside, dolomite, synthetic enstatite, bronzite, talc, tremolite and wollastonite have been determined to an accuracy of ±1.0 percent by differential scanning calorimetry between 350 and 1000 K. The CPo measurements for anthophyllite were also corrected to a composition of pure Mg-anthophyllite [Mg7Si8O22(OH)2]. These heat capacities were combined with existing low-temperature heat capacity, entropy, and high-temperature relative enthalpy data, and fitted by least squares to the following equations [T, in kelvin; CPo, in J/(mol · K)]:

Magnesio-anthophyllite [Mg6.3Fe0.7Si8O22(OH)2], (298–700 K)
CPo=32871.628T1.885×107T241859T0.5+6.527×104T2
Magnesio-anthophyllite [Mg7Si8O22(OH)2], (298–700 K)
CPo=27130.9630T+1.331×107T233473T0.5+2954×104T2
Diopside [CaMg(SiO3)2], (298–1600 K)
CPo=470.250.09864T+2.453×105T24823T0.5+2.813×105T2
Dolomite [CaMg(CO3)2], (298–650 K)
CPo=547.90.1676T+2.840×106T26548T0.5+7.708×105T2
Enstatite (synthetic MgSiO3), (298–1000 K)
CPo=350.70.1473T+1.679×106T24296T0.5+5.826×105T2
Bronzite (Mg0.85Fe0.15SiO3), (298–1000 K)
CPo=207.90.01489T+1.921×105T22135T0.5
Talc [Mg3Si4O10(OH)2], (298–650 K)
CPo=79637.513T+6.505×107T21.117×105T0.5+3.806×103T2
Tremolite [Ca2Mg5Si8O22(OH)2], (298–800 K)
CPo=61314.189T+5.139×107T28.566×104T0.5+1.757×103T2
Wollastonite (CaSiO3), (298–1400 K)
CPo=200.80.02590T1.579×105T21826T0.5+7.435×106T2

By combining our calorimetric data with a high-temperature heat-of-solution value and ancillary thermodynamic data, we calculate ΔHf.298o and ΔGf.298o (based on the elements) for enstatite as − 1549.60 ± 2.50 and −1462.10±2.50 kJ/mol, respectively.

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