High-pressure compressibility and phase stability of Mn-dolomite (kutnohorite)

Abstract

We measured the bulk modulus and phase stability of a natural Mn-dolomite, kutnohorite, to 19 GPa. At room temperature, kutnohorite is stable in the rhombohedral dolomite phase up to 19 GPa, with an isothermal bulk modulus of 85(6) GPa (Kʹ = 4). The compressibility of kutnohorite is found to match well with both single and double carbonate trends with respect to bulk modulus and unit-cell volume. The thermoelastic properties measured in this study show that the Mn dolomite end-member fits well with the systematic of all the rhombohedral carbonates, both calcite (single carbonate) and dolomite (double carbonate) type.

A high-pressure structural transition of norsethite-type BaFe(CO3)2: Comparison with BaMg(CO3)2 and BaMn(CO3)2

“…The phase transition pressures of BaMg(CO 3 ) 2 , BaFe(CO 3 ) 2 , and BaMn(CO 3 ) 2 are 2.4(2), 2.7(5), and 3.9(2) GPa in this study, respectively. Compared with this study and previous results (Lin et al 2012;Spivak et al 2014;Cerantola et al 2015;Merlini et al 2015;Palaich et al 2015;Fu et al 2017;Merlini et al 2017;Vennari and Williams 2018;Binck et al 2020;Chariton et al 2020;Wang et al 2022), the phase stability of norsethite-type Ba(Mg,Fe,Mn)(CO 3 ) 2 , dolomite-type Ca(Mg,Fe,Mn)(CO 3 ) 2 , and calcite-type (Mg,Fe,Mn)CO 3 carbonates at ambient temperature were presented in Figure 7. The effective cation radii of Ba 2+ , Ca 2+ , Mn 2+ , Fe 2+ , and Mg 2+ are 1.35, 1.00, 0.83, 0.78, and 0.72 Å at ambient conditions, respectively (Shannon and Prewitt 1969).…”

“…Compared to the norsethite-type family BaMg(CO 3 ) 2 , the K 0 of α-BaFe(CO 3 ) 2 is distinctly smaller than that of α-BaMg(CO 3 ) 2 (K 0 = 66.2 GPa) (Pippinger et al 2014). Different from the comparable K 0 values of dolomite-type carbonates, the K 0 values are 95(1), 92(1), and 85(6) for CaMg(CO 3 ) 2 , CaMg 0.6 Fe 0.4 (CO 3 ) 2 , and Ca 0.76 Mn 1.24 (CO 3 ) 2 , respectively (K 0 ′= 4) (Merlini et al 2017;Palaich et al 2015). It may be attributed to the existence of superlattice in α-BaMg(CO 3 ) 2 , which greatly improves its incompressibility (Helmersson et al 1987;Pippinger et al 2014;Dong et al 2015).…”

“…Partial cation substitution in carbonates is very common in natural samples, and the effects of substitution with various compositions and proportions on the physical and chemical properties of carbonates were extensively studied (e.g., Reeder and Dollase 1989;Lin et al 2012;Palaich et al 2015;Cerantola et al 2017;Zhao et al 2020;Gabitov et al 2021). Mn 2+ or Fe 2+ cations can often be incorporated into the crystal structures in double carbonates, such as kutnahorite, ankerite, and norsethitetype BaMn(CO 3 ) 2 (Rividi et al 2010;Efthimiopoulos et al 2017;Wang et al 2022).…”

Effects of hydrostaticity and Mn-substitution on dolomite stability at high pressure

“…(Binck et al, 2020b), it is denoted as the Dol-Ⅱ phase in this study. Moreover, Palaich et al (2015) reported a dramatic increase in the volume of Mn-rich dolomite sample Ca 0.76 Mn 0.1.24 (CO 3 ) 2 in a neon PTM at 15.9 GPa, associated with the disappearing and splitting of several diffraction lines in the powder x-ray diffraction (XRD) patterns. To some extent, this result supports the phase transition of Mn-dolomite revealed in the high-pressure evolution of Raman spectra in this study.…”