Hydrous ferric sulfate Fe(SO4)(OH) ∙ 2H2O from the supergene zone of the Khangalas gold deposit, Eastern Yakutia, Russia

Kudrin M. V., Zayakina N. V., Fridovsky V. Yu., Galenchikova L. T.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2020. V. 149. N 3. P. 126-141


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Language: English 


A hydrous ferric sulfate with a formula Fe(SO4)(OH) ∙ 2H2O was discovered in the supergene zone of the Khangalas gold ore deposit, Yakutia, Russia. Studies of the mineral showed that it has no analogues among natural and synthetic compounds. The mineral is beige-yellow in color, very soft, with a fibrous texture and a finely crystalline structure. It occurs as veinlets and nest-like aggregates (up to 5–6 cm in size) of thin, elongate, acicular crystals ≤1 μm across and ≤20 μm in length. Associated minerals are quartz, jarosite, muscovite, and anorthite. The chemical composition (wet-chemical analysis in wt %) is as follows: Fe2O3 37.82, SO3 37.84, H2O 22.70, SiO2 0.26, Al2O3 0.38, total 99.00. The empirical formula calculated on the basis of one S atom per formula unit (apfu) is Fe1.002(SO4)(OH) · (H4.33O2.18). The simplified formula Fe(SO4)(OH) · 2H2O requires Fe2O3 38.96, SO3 39.07, Н2O 21.97, total 100.00 wt %. The unit-cell parameters were refined by the least squares method for the full X-ray pattern. A triclinic cell with parameters a = 7.30(1), b = 10.96(2), c = 11.70(2) Å, α = 108(1)°, β = 102.1(4)°, γ = 97.0(2)°, V = 853(8) Å3, Z = 6 was chosen from among the various possible variants, space group P1, P (?). The strongest X-ray powder diffraction lines [d, A (I, %) (hkl)] are: 10.72 (100) (001), 10.22 (80) (010), 9.12 (28) (0–11), 5.356 (8) (002), 4.108 (10) (–1–21), 3.758 (9) (1–22), 3.476 (4) (0–32). The mineral is chemically close to polymorphic modifications of the hydrous ferric sulfate Fe(SO4)(OH)∙2H2O: butlerite and parabutlerite, but differs from them in the X-ray powder diffraction pattern and IR and Raman spectra. These facts served as the basis for a detailed study of the mineral. Due to the fine-fibrous texture and poor quality of X-ray diffraction reflections, the crystal structure of the found sulfate has not been resolved. It was the main reason why the mineral was not approved by the Commission on New Minerals and Mineral Names of the International Mineralogical Association (CNMMN, IMA).

Keywords: hydrous ferric sulfate, butlerite, parabutlerite, X-ray powder diffraction pattern, IR and Raman spectra, supergene zone, permafrost, Khangalas deposit, Yakutia