Tinnunculite, C5H4N4O3 • 2Н2O: finds at Kola Peninsula, redefinition and validation as a mineral species

Pekov I. V., Chukanov N. V., Yapaskurt V. O., BeJakovskiy D. L, Lykova I. S., Zubkova N. V., Shcherbakova E. P., Britvin S. N., Chervonnyi A. D.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2016. V. 145. N 4. P. 20-35

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Language: Russian


Based on results of the study of samples found in Khibiny (Mt. Rasvumchorr: the holotype) and Lovozero (Mts Alluaiv and Vavnbed) alkaline complexes at Kola Peninsula, Russia, tinnunculite was accepted by the IMA Commission on New Minerals, Nomenclature and Classification as valid mineral species (IMA No. 2015-02la) and, taking into account the revision examination of the original ma terial from burnt dumps of coal mines at South Urals, Russia, it was redefined as a crystalline uric acid dihydrate (UAD), C5H4N4O3 · 2H2O. Tinnunculite was formed as a product of the mineralization of bird excrements in the biogeochemical systems which could be defined as «guano microdeposits». The mineral occurs as prismatic or tabular crystals, up to mm in size, and their clusters, as well as crystalline or micro-globular crusts. Tinnunculite is transparent or translucent. It is colorless, white, yellowish, reddish or pale lilac. Crystals show vitreous luster. The mineral is soft and brittle, with distinct (010) cleavage. Dcalc = 1.68 g/cm3 (holotype). Tinnunculite is optically biaxial (–), α = 1.503(3), β = 1.712(3), γ = 1.74(1), 2Vmeas = 40(10)°. The IR spectrum is reported. Chemical composition of the holotype sample (wt %; electron microprobe data, content of H is calculated by UAD stoichiometry) is: Î 37.5, Ñ 28.4, N 27.0, Hcalc 3.8, total 96.7. The empirical formula calculated based on (C+N+O) = 14 apfu is: C4.99H8N4.07O4.94. Tinnunculite is monoclinic, sp. gr. (by analogy with synthetic UAD) P21/c. Unit cell parameters of the holotype sample (single-crystal XRD data) are: a = 7.37(4), b = 6.326(16), c = 17.59(4) Å, β = 90(1)°, V= 820(5) Å3, Z = 4. The strongest reflections of the powder XRD pattern (d,Å—I[hkl]) are: 8.82—84[002]; 5.97—15[011]; 5.63—24[102, 102]; 4.22—22[112]; 3.24—27[114,114], 3.18—100[210], 3.12—44[211, 211], 2.576—14[024].

Key words: tinnunculite, new mineral, organic mineral, uricite, uric acid dihydrate, guano mineralization, Khibiny, Lovozero, Kopeisk.