Abstract:
Barsanovite, described in 1963 as a monoclinic dimorph of trigonal eudialyte, was discredited in 1969 because its assignment to the monoclinic system had been proved to be erroneous. Revision study of the barsanovite type specimen carried out with use of the X-ray single crystal analysis has shown that the mineral is the trigonal one and has a distinct combination of cations and anions that are dominant in the key sites of the crystal structure. It means that this mineral deserves to be revalidated as a separate mineral species of the eudialyte group. According to this proposal, the mineral was revalidated in 2003 by the IMA CNMMN with the new name georgbar-sanovite given as before after Georg Barsanov (1907-1991), the known Russian mineralogist. Thus, the original term «barsanovite» become a synonym of georgbarsanovite. The mineral is transparent or translucent; color yellow-green; streak white; luster vitreous; Mohs' hardness 5; brittle; fracture uneven to conchoidal; no cleavage observed. £»mcas= 3.05(2), £>Ыс= 3.11 g/cm3. Optically uniaxial, negative, N0 = 1.639(2), Ne= 1.631(2); ple-ochroic: N0 green, Ne pale yellow. Trigonal, space group RT>m, a - 14.262(2), с = 29.949(4) A, V= 5276(2) A3. Strongest XRD lines [d. A, (I) (hkl)]: 3.202(100)(208), 2.975(98)(315), 2.857(94)(404), 3.155(71X217), 4.304(62)(205), 6.42(54X104), 2.591(54X039), 3.179(52)(306), 3.017(52)(119). Empirical formula at £cat = = 53, Z=3: (Na| 1.73 Ko.24ki 1.97 (Мп1.]9$Го.7| REEo.63CaojoYo.i3Bao.o3)i2.99Ca6(Fe255Zrq23Ti<).osHfo.o4)5:2.87 Zr3Nbo.92Si25.25O76.48Cli.iiF06| 0.88H2O (microprobe data, H2O by wet chemistry). Simplified formula: Na)2 (Mn, Sr, REE)3Ca6Fe3+Zr3NbSi25O76Cl2-H2O. IR spectrum is given. Crystal structure is determined, R = = 0.0365.