Karupmollerite-Ca, (Na,Ca,K)2Ca(Nb,Ti)4 (Si4O12)2(O,OH)47H2O, a new mineral of the labuntsovite group from the Ilimaussaq alkaline complex, South Greenland
Pekov, I.V.; Chukanov, N.V.; Petersen, O.V.; Zadov, A.E.; Yamnova, N.A.; Kabalov, Y.K.; Schneider, J.
published: Oct 21, 2002
Karupmøllerite-Ca, a new mineral species of the labuntsovite group, was found in hydrothermally altered areas in one complex naujaite pegmatite in the Mellemelv stream valley, Kangerluarsuk area, Ilímaussaq alkaline complex, South Greenland. It forms large - up to 2 × 1.5 × 0.1cm - pseudomorphs after lamellae of epistolite replacing vuonnemite, and is associated with aegirine, albite, arfvedsonite, carbonate-fluorapatite, eudialyte, lueshite, natrolite, potassic feldspar, sodalite, and tuperssuatsiaite. The aggregates of karupmøllerite-Ca with relics of epistolite are translucent, white with greyish and pinkish tints, the lustre vitreous to dull. They are brittle, Mohs' hardness = 5. Particles of karupmøllerite-Ca, about 0.01 mm in size, are irregular, platy. Dmeas = 2.71(1), Dcalc = 2.74g/cm3. Optically karupmøllerite-Ca is biaxial (+), 2Vmeas = 30 ± 15°, 2Vcalc = 29.7°; α = 1.656(2), β = 1.662(2) and γ = 1.755(3). It is non-pleochroic and shows no cleavage, dispersion has not been observed. The IR spectrum includes the following strong bands (cm-1): 3360, 1630, 1138, 948, 680, 455. Electron microprobe, H2O by TGA, gave: Na2O 2.17, K2O 1.74, CaO 6.00, SrO 0.08, BaO 0.28, MnO 0.3 , ZnO 0.06, Fe2O3 0.47, Al2O3 0.25, SiO2 39.85, TiO2 8.51, Nb2O5 29.92, H2O 11.31, Total 100.95 wt.%. The empirical formula, based on [(Si,Al)8O24](O,OH)4, is (Na0.84Ca0.64K0.44Ba0.02 Sr0.01)Σ1.95(Ca0.64Mn0.05Zn0.01)Σ0.70(Nb2.70Ti1.28Fe3+0.07)Σ4.05 (Si7.94Al0.06)Σ8O24 [O2.75(OH)1.25]Σ4·6.94H2O, the idealized formula (Na,Ca,K)2Ca(Nb,Ti)4(Si4O12)2 (O,OH)4·7H2O, Z = 2. The strongest lines of the X-ray powder diffraction pattern [d in Å (I) (hkl)] are: 7.104(73)(020), 7.026(100)(001), 6.482(45)(201¯), 4.996(74) (021¯, 021); 3.253(38)(421¯), 3.171(56)(041¯), 3.150(38)(022¯, 022). Karupmøllerite-Ca is monoclinic, space group C2/m, with a = 14.641(1), b = 14.214(1), c = 7.9148(2) Å, β = 117.36(1)°, V = 1463(2) Å3. The crystal structure was studied by Rietveld method, final value of R = 0.039. The structure is based on a framework consisting of corrugated columns of M-(O,OH) octahedra (M = Nb > Ti,Fe) connected by (Si4O12) rings and D octahedra occupied with Ca - occupancy degree 70%. Large cations, prevailing Na and water molecules, are situated in zeolite-like cavities. The name honours the Danish mineralogist Svend Karup-Møller (1936), associate professor at the Technical University of Denmark, who first found this mineral. Both the mineral and the name have been approved by the Commission on New Minerals and Mineral Names of the International Mineralogical Association. Type specimens are deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, and at the Geological Museum, Copenhagen.