Reynoldsite from the Oxidation Zone of the Tochilnogorskoe Deposit (Middle Urals)—The First Find in Russia

Our study of the historical Tochilnogorskoe deposit of refractory stone (Tochilnaya Mountain) in the Rezhevsky district, Middle Urals, has revealed for the first time in Russia a very rare lead chromate oxide, reynoldsite Pb_2Mn₂^4 + O5(CrO4), which was previously discovered in only three locations worldwide. Reynoldsite was found in a muscovite aggregate with secondary Pb–Mn oxides in fractures of veiny quartz, as well as in druse cavities of quartz veins, with crocoite and goethite pseudomorphs after pyrite. The mineral forms elongated, plate-like individuals up to 10 µm in size and monomineralic, tangled fibrous aggregates up to 0.3 mm in size overgrowing cesarolite, muscovite, and quartz. The empirical formula of reynoldsite demonstrates the range Pb2.00–2.06 Mn_2.01 - 2.06^4 + O5(Cr0.96–0.98O4). The strongest reflections of the powder X-ray diffraction pattern [d, Å(I)] are: 3.060 (100), 3.233 (75), 4.688 (68), 3.004 (64), 3.351 (54), 2.498 (53), 2.912 (44). The mineral is triclinic, space group P-1; unit cell parameters are: a = 5.013(3) Å, b = 7.589(9) Å, c = 10.254(5) Å; α = 91.86(6)°, β = 99.65(4)°, γ = 109.08(6)°; V = 361.9(4) Å3, Z = 2. The Raman spectrum is presented for the first time for reynoldsite, it can be used to identify the mineral. Reynoldsite is a supergene mineral formed as a result of the weathering of primary minerals (galena in quartz and chromespinelides in host ultramafic rocks).