Eur. J. Mineral., 33, 357–371, 2021 https://doi.org/10.5194/ejm-33-357-2021 © Author(s) 2021. This work is distributed under the Creative Commons Attribution 4.0 License. Chapmanite [Fe2Sb(Si2O5)O3(OH)]: thermodynamic properties and formation in low-temperature environments Juraj Majzlan1, Stefan Kiefer1, Kristina Lilova2, Tamilarasan Subramani2, Alexandra Navrotsky2, Edgar Dachs3, and Artur Benisek3 1Institute of Geosciences, Friedrich Schiller University, Burgweg 11, 07749 Jena, Germany 2School of Molecular Sciences and Center for Materials of the Universe, Arizona State University, Tempe, Arizona 85287, USA 3Department of Chemistry and Physics of Materials, University of Salzburg, Jakob-Haringer-Str. 2a, 5020 Salzburg, Austria Correspondence: Juraj Majzlan (
[email protected]) Received: 18 March 2021 – Revised: 1 June 2021 – Accepted: 4 June 2021 – Published: 2 July 2021 Abstract. In this work, we have determined or evaluated thermodynamic properties of synthetic Sb2O5, MgSb2O6 (analogue of the mineral byströmite), Mg[Sb(OH)6]2 · 6H2O (brandholzite), and natural chapman- ite [(Fe1:88Al0:12)Sb(Si2O5)O3(OH)]. Enthalpies of reactions, including formation enthalpies, were evaluated using reference compounds Sb, Sb2O3, Sb2O5, and other phases, with high-temperature oxide melt solution calorimetry in lead borate and sodium molybdate solvents. Heat capacity and entropy were determined by relax- o −1 o −1 −1 ation and differential scanning calorimetry. The best set of 1f H (kJ mol ) and S (J mol K ) is byströmite −1733:0±3:6, 139:3±1:0; brandholzite −5243:1±3:6, 571:0±4:0; and chapmanite −3164:9±4:7, 305:1±2:1. o −1 The data for chapmanite give 1f G of −2973:6 ± 4:7 kJ mol and logK D −17:10 for the dissolution reac- C C ! 3C C 3C C 0 C 0 C tion (Fe1:88Al0:12)Sb(Si2O5)O3(OH) 6H 1.88Fe 0.12Al 2SiO2 Sb(OH)3 2H2O.