Gjerdingenite-Mn from Norway - A new mineral species in the labuntsovite group: Descriptive data and crystal structure

Author(s)
Gunnar Raade, N V Chukanov, Uwe Kolitsch, Steffen Möckel, Aleksandr E. Zadov, Igor V Pekov
Abstract

Gjerdingenite-Mn occurs as orange-yellow to brownish prisms up to 1 mm long in miarolitic cavities of a sodic granite ('ekerite') at Gjerdingselva, Lunner, Oppland, Oslo Region, Norway. The simplified formula is (K,Na)2(Mn,Fe) [(Nb,Ti)4(Si 4O12)2(O,OH)4]ž 6H2O. It is the Mn-dominant analogue of gjerdingenite-Fe, the Ti analogue of kuzmenkoite-Mn and a dimorph of organovaite-Mn. The mineral is monoclinic, C2/m, with a = 14.563(3), b = 13.961(3), c = 7.851(2) A°, ß = 117.62(3)°, V = 1414.3(6) A° 3, Z = 2. The crystal structure was refined to R(F) = 0.079 on the basis of 1207 observed reflections and is compared to the structure of gjerdingenite-Fe. The strongest five reflections of the X-ray powder-diffraction pattern [dobs in A° (I) (hkl)] are: 6.96 (100) (020, 001), 4.94 (80) (021), 3.22 (90) (42-1, 400, 40-2 , 3.10 (80) (041, 022) and 2.510 (40) (44-1, 401, 40-3, 042). The mineral is optically biaxial (+) with a = 1.670(2), ß = 1.685(2), ? = 1.775(5); 2Vmeas = 52(8)°, 2Vcalc = 46(5)°. The axial dispersion is weak, r <v; the orientation is Z = a, Y = b. Mohs hardness is about 5; Dcalc = 2.93 g/cm 3. The pseudo-orthorhombic crystals are twinned on {001}, elongate along [010] and show the forms {001}, {100}, {201} and {021}. Some general aspects on the formation of labuntsovite-group minerals are discussed. Œ 2004 E. Schweizerbart'sche Verlagsbuchhandlung.

Organisation(s)
Department of Mineralogy and Crystallography
External organisation(s)
University of Oslo, Russian Academy of Sciences, NPO Regenerator, Anuchin Research Institute and Museum of Anthropology
Journal
European Journal of Mineralogy: an international journal of mineralogy, geochemistry and related sciences
Volume
16
Pages
979-987
No. of pages
9
ISSN
0935-1221
Publication date
2004
Peer reviewed
Yes
Austrian Fields of Science 2012
1051 Geology, Mineralogy
Portal url
https://ucrisportal.univie.ac.at/en/publications/0036bcd7-b17c-4d53-9084-52aff2cb970e