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Karchevskyite, [Mg18Al9(OH)54][Sr2(CO3,PO4)9(H2O,H3O)11], a new mineral species of the layered double hydroxide family |
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| Authors: | S N Britvin N V Chukanov G K Bekenova M A Yagovkina A V Antonov A N Bogdanova N I Krasnova |
| Institution: | 1. Faculty of Geology, St. Petersburg State University, Universitetskaya nab. 7/9, St. Petersburg, 199034, Russia 2. Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow oblast, 142432, Russia 3. Satpaev Institute of Geology, ul. Kabanbai-Batyr 69a, Almaty, 480100, Kazakhstan 4. Ioffe Physicotechnical Institute, Russian Academy of Sciences, ul. Politekhnicheskaya 26, St. Petersburg, 194021, Russia 5. Center of Isotopic Studies, Russian Geological Research Institute, Srednii pr. 74, St. Petersburg, 199106, Russia 6. Geological Institute, Kola Science Center, Russian Academy of Sciences, ul. Fersmana 14, Apatity, 184200, Russia |
| Abstract: | Karchevskyite, a new mineral related to the family of layered double hydroxides (LDHs), has been found in the Iron open pit at the Kovdor carbonatite massif, Kola Peninsula, Russia. The mineral occurs as spherulites of up to 1.5 mm in diameter composed of thin, curved lamellae. Dolomite, magnetite, quintinite-3T, strontium carbonate, and fluorapatite are associated minerals. Karchevskyite is white in aggregates and colorless in separate platelets. Its luster is vitreous with a pearly shine on the cleavage surface. The new mineral is nonfluorescent. The Mohs hardness is 2. The cleavage is eminent (micalike), parallel to {001}. The measured density is 2.21(2) g/cm3, and the calculated value is 2.18(1) g/cm3. Karchevskyite is colorless and nonpleochroic in immersion liquids. It is uniaxial, negative, ω = 1.542(2), and ? = 1.534(2). The chemical composition (electron microprobe, average of ten point analyses, standard deviation in parentheses, wt %) is as follows: 29.7(1.1) MgO, 18.3(0.7) Al2O3, 7.4(0.4) SrO, 0.2(0.1) CaO, 1.3(0.2) P2O5, 14.5(0.4) CO2, and 28.6 H2O (estimated by difference); the total is 100. The empirical formula calculated on the basis of nine Al atoms is Mg18.00Al9.00(OH)54.00(Sr1.79Mg0.48Ca0.09)2.36 (Ca3)8.26(PO4)0.46(H2O)6.54(H3O)4.18. The idealized formula is Mg18Al9(OH)54]Sr2(CO3, PO4)9(H2O, H3O)11]. The new mineral slowly dissolves in 10% HCl with weak effervescence. Karchevskyite is trigonal; possible space groups are P3, P3, P $ \overline 3 
1m, P31m, P312, P312, P3m1, or P3m1; unit-cell dimensions are a = 16.055(6), c = 25.66(1) ?, V = 5728(7) ?3, Z = 3. The strongest reflections in the X-ray powder diffraction pattern d, (I, %)(hkl)] are: 8.52(10)(003), 6.41(4)(004), 5.13(3)(005), 4.27(6)(006), 3.665(9)(007), 3.547(9)(107), 3.081(6)(315). Wavenumbers
of absorption bands in the infrared spectrum of the new mineral are (cm−1; s is shoulder): 3470, 3420s, 3035, 2960s, 1650, 1426, 1366, 1024, 937, 860, 779, 678, 615s, 553, 449, 386. Results of thermogravimetric
analysis: total weight loss is 42.0 wt %, with three stages of loss: 12.2%, maximum rate at 230°C; 6.1%, maximum rate at 320°C;
and 23.7%, maximum rate at 440°C. Karchevskyite is a late-stage hydrothermal mineral. The mineral is named in memory of Russian
mineralogist Pavel Karchevsky (1976–2002), who made a significant contribution to the study of carbonatites. The type material
of karchevskyite is deposited at the Mineralogical Museum, Division of Mineralogy, St. Petersburg State University, and the
Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow.
Original Russian Text ? S.N. Britvin, N.V. Chukanov, G.K. Bekenova, M.A. Yagovkina, A.V. Antonov, A.N. Bogdanova, N.I. Krasnova,
2007, published in Zapiski Rossiiskogo Mineralogicheskogo Obshchestva, 2007, No. 5, pp. 44–56.
The new mineral karchevskyite and its name accepted by the Commission on New Minerals and Mineral Names, Russian Mineralogical
Society, March 21, 2005. Approved by the Commission on New Minerals and Mineral Names, International Mineralogical Association,
June 30, 2005. |
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