Akopovaite, Li2Al4(OH)12(CO3)(H2O)3, a new Li member of the hydrotalcite supergroup from Turkestan Range, Kyrgyzstan

Vladimir Yu Karpenko, Elena S. Zhitova, Leonid A. Pautov, Atali A. Agakhanov, Oleg I. Siidra, Maria G. Krzhizhanovskaya, Victor A. Rassulov, Vladimir N. Bocharov

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Abstract

Akopovaite, ideally Li2Al4(OH)12(CO3)(H2O)3, is a new hydrotalcite-supergroup mineral from the Karasu-Karavshinskoye Sn deposit, Turkestan Range, Kyrgyzstan. It occurs as white or pale yellowish rosette-like aggregates that are composed of tiny curved plates up to 20-30 μm. Akopovaite is associated with gibbsite, quartz, albite, microcline, muscovite, montebrasite, siderite, schorl and birnessite-like Fe-Mn oxides. Akopovaite has a perfect cleavage along {001}, the mineral is transparent and very soft (VHN = 24 that corresponds to Mohs hardness of ca. 1). Dmeas = 2.12(2) g/cm3 and Dcalc = 2.106 g/cm3. The Raman spectra contain bands of carbonate groups and bands of O-H stretching vibrations. The chemical composition (wt.%, electron microprobe for Al and Fe; ICP-OES for Li; CHN method for CO2 and H2O) is Li2O 6.43, Al2O3 45.79, Fe2O3 0.27, CO2 10.09, H2O 36.1, total 98.68. The empirical formula based on (Li + Al + Fe) = 6 apfu is Li1.94(Al4.05Fe0.02)Σ4.07(OH)12(CO3)1.03(H2O)3.03. The crystal structure was refined by the Rietveld method with RB = 0.006 and Rwp = 0.014. Akopovaite is monoclinic, C2/m, a = 5.0953(6), b = 8.877(1), c = 7.806(1) Å, β = 102.572(6)°, V = 344.61(8) Å3 and Z = 1. The polytype should be denoted as 1M. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 7.66(100)(001), 4.397(27)(020), 3.821(45)(002,021), 2.4881(27)(200), 2.2273(16)(201) and 1.9027(18)(202). Akopovaite is the first naturally occurring hydrotalcite-supergroup carbonate species of Al and Li; its synthetic analogue is known.

Original languageEnglish
Pages (from-to)301-311
Number of pages11
JournalMineralogical Magazine
Volume84
Issue number2
DOIs
StatePublished - 1 Apr 2020

Scopus subject areas

  • Geochemistry and Petrology

Keywords

  • akopovaite
  • carbonate
  • dritsite
  • hydrotalcite supergroup
  • Karasu-Karavshinskoye Sn deposit
  • layered double hydroxides
  • new mineral
  • polytype
  • quintinite
  • Turkestan Range

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