Vol 70, No 5 (2025)

The comprehensive physicochemical study of babingtonite Ca_2.0(Mg_0.2)_∑1.0Si₅O₁₄(OH)_1.0 (Herborn, Hessen, Germany) was carried out using powder X-ray diffraction, electron probe microanalysis, IR, Raman and Mössbauer spectroscopy. The enthalpy of formation of the studied babingtonite from the elements was determined for the first time using high-temperature solution calorimetry on a Calvet microcalorimeter in a melt of the composition 2PbO∙B₂O₃ at T = 973 K (–6911.6 ± 10.2 kJ/mol). The value of its standard entropy was estimated and the values of the standard entropy and Gibbs energy of formation were calculated (338.8 ± 2.0 J/(mol K), −1501.3 ± 2.0 J/(mol K) and − 6464.0 ± 10.2 kJ/mol, respectively). The thermodynamic constants of the end members of the isomorphic series babingtonite Ca₂Fe²⁺Fe³⁺Si₅O₁₄(OH) − manganbabingtonite Ca₂Mn²⁺Fe³⁺Si₅O¹⁴(OH): were estimated: _f(298.15 K) = −6868.0 ± 10.4 and −6876.9 ± 9.9 kJ/mol, S°(298.15 K) = 341.2 ± 1.8 and 343.9 ± 2.6 J/(mol. K), Δ_f(298.15 K) = −1496.8 ± 1.8 and –1499.0 ± 2.6 J/(mol K), Δ_fG(298.15 K) = −6422.0 ± 10.4 and −6430.0 ± 9.9 kJ/mol, respectively. The stability fields of babingtonite for oxidation-reduction conditions determined by two different buffers − quartz-fayalite-magnetite and magnetite-hematite − in P_H2O − t coordinates, as well as mineral associations of babingtonite in lgP_CO2 – lgP_O2 coordinates, characteristic of low-grade metamorphism and late skarn parageneses, were calculated.

The features of distribution and composition of organic of abiotic (C_org; HC; C_HC/C_org, %) and biotic (phytopigments, microbial communities) components of soils and bottom sediments (BS) formed under conditions of long-term anthropogenic transformation of the landscape were studied. Average concentrations of C_org in soils and bottom sediments did not differ significantly and varied at the level of 4.9 %. The HC content in soils was 20–560, in BS – 3–20 in mg/kg. In BS, the amount of chlorophyll (chl.) a was 1.4–6.0, chl. b up to 2.8, chl. c up to 3.9 μg/g. In the soil, chl. a did not exceed 4.4, chl. b 2.8, chl. c 3.9 μg/g. Carotenoids dominated in the composition of phytopigments and varied from 6.8 to 12.2 μg/g in sediments and from 4.1 to 9.5 μg/g in soils. The share of primary production carbon in the composition of C_org in river sediments was 0.01–1.36 % and from 0.18 to 0.76 % in soils, which is 1–2 orders of magnitude higher than the share of HC. Diatoms was found to actively participate in the production of organic matter (OM) in river sediments. At the level of molecular markers, a more significant role of primary production of microalgae in the formation of organic matter in soils and BS was revealed compared to higher vegetation. The leading role in the formation of OM in soils and sediments belongs to the microbial-destructive component (∑C₂₀–C₂₅ = 33.9–48.2 %), which is consistent with the relatively high (up to 63.6 %) share of hydrocarbon-oxidizing bacteria in microbial communities. It has been shown that during secondary soil formation on ash dumps, a significant role in the formation of organic matter belongs to microalgae: the proportion of the corresponding markers (∑С₁₅, С₁₇, С₁₉) reached 42.6 % of the total n-alkanes.