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Chukanovite, Fe₂(CO₃)(OH)₂, a new mineral from the weathered iron meteorite Dronino

¹ Faculty of Geology, Moscow State University, Vorobievy Gory, 119992 Moscow, Russia
² Dipartimento di Scienze della Terra, Università di Pisa, via S. Maria 53, 56126 Pisa, Italy
³ Dipartimento di Scienze della Terra, Università degli Studi di Milano, via Botticelli, 23, 20133 Milano, Italy
⁴ NPO Regenerator, 3^rd Passage of Mar’ina Roshcha 40, 127018 Moscow, Russia

^* Corresponding author, e-mail: igorpekov{at}mail.ru

The new mineral chukanovite, Fe₂(CO₃)(OH)₂, occurs in cavities of weathered fragments of the Dronino ataxite iron eteorite found near the Dronino village, Kasimov district, Ryazan’ Oblast, Russia. It is a product of terrestrial alteration of meteorite iron. Associated minerals are goethite, akaganéite, hematite, hibbingite, reevesite, honessite, etc. Chukanovite forms acicular to fibrous individuals (up to 0.5 mm long and up to 2–3 µm thick) combined in spherulites up to 1 mm in diameter, botryoidal spherulitic clusters and parallel- or radial-columnar aggregates which form crusts up to 1 mm thick. Unaltered chukanovite is transparent, pale-green or colourless. The surface of aggregates is brownish-green. Streak is white. Lustre is vitreous. Cleavage is perfect, probably on {0–21}, fracture is uneven. The mineral is brittle, the Mohs’ hardness is 3.5–4, the calculated density is 3.60 g/cm³. It is optically biaxial (–) with 1.673(3), β1.770(5), 1.780(5), 2V_meas. 10(5)°. Average chemical composition (wt. %; electron probe, H₂O by modified Penfield method, CO₂ by selective sorption) is: MgO 0.1, FeO 68.8, NiO 0.6, CO₂ 19.8, H₂O 10.9, total 100.2. The empirical formula calculated on the basis of two metal atoms is (Fe²⁺_1.97Ni_0.02Mg_0.01)_2.00(CO₃)_0.93(OH)_2.14·0.18H₂O, ideally Fe₂(CO₃)(OH)₂. Chukanovite is monoclinic P2₁/a, with a = 12.396(1) Å, b = 9.407(1) Å, c = 3.2152(3) Å, β = 97.78°. The strongest lines of the X-ray powder pattern [d(Å), I, (hkl)] are: 6.14, 40, (200); 5.15, 60, (231); 3.73, 80, (310); 2.645, 100, (230); 2.361, 40, (510); 2.171, 40, (520). The structure of chukanovite was refined on synchrotron data by the Rietveld method up to Rp = 3.43 %, wRp = 4.51 %, R_Bragg = 2.48 %. Chukanovite is closely related to the minerals of the malachite-rosasite group. It was named in honour of Nikita V. Chukanov (b. 1953), Russian physicist and mineralogist. The holotype specimen is deposited in the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow.

Key-words: chukanovite, new mineral, iron hydroxide-carbonate, malachite-rosasite group, Rietveld refinement, Dronino meteorite.