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IMA 2010-089 = perrierite-(La)

Posted by Marco E. Ciriotti  
avatar IMA 2010-089 = perrierite-(La)
March 05, 2012 03:32PM
Referenza:
▪ Chukanov, N.V., Blass, G., Pekov, I.V., Belakovskiy, D.I., Van, K.V., Rastsvetaeva, R.K., Aksenov, S.M. (2011): Perrierite-(La)(La,Ce,Ca)4Fe2+(Ti,Fe)4(Si2O7)2O8 - a new mineral species from volcanic region Eifel, Germany. Zapiski RMO, 140, 34-44.

Abstract:
Non-metamict perrierite-(La) bad been found in the in den Dellen pumice quarry, near Mendig, Laacher See area, Eifel Mountains, Rhineland-Palatinate (Rheinland-Pfalz), Germany; and has been approved as a new mineral species (IMA No. 2010-089). Associated minerals are sanidine, phlogopite, pyrophanite, zirconolite, members of the jakobsite-magnetite series, fluorocalciopyrochlore and zircon. Perrierite-(La) occurs as isolated prismatic crystals up to 0.5 X I mm in size in cavities in sanidinite. The mineral is brittle, with Mohs' hardness of 6 and distinct cleavage on (001). Color is black, streak is brown. D„lc = = 4.791 g/cm3. IR spectrum shows the absence of H20 and OH groups. Perierite-(La) is biaxial {—), о =* 1»:94(I), p = 2.020{15), у = 2.040( 15), 2 Vmm — 50( 10)°, 2УЫс = 51°. Chemical composition (electron microprobe, mean of 7 point analyses, the ratio Fe3+ ; Fe2+ determined from structural data, wt%) is: CaO 3.26, La2O3 22.92, Се2O3 19.64, Рг2O3 0.83, Nd2O3 2.09, MgO 0.25, MnO 2.25, FeO 3.16, Fe2O3 5.28, Аl2O3 2.59, TiO2 16.13, Nb2O5 0.75, SiO2 20.06, total sum 99.21. The simplified formula is (La,Ce,Ca)4Fe2+(Ti,Fe3+)4[(Si2O7)O4]2. The crystal structure was refined on a single crystal. Perrierite-(La) is monoclinic, space group P21/a unit-cell parameters are: a = 13.668(1), b = 5.6601(6), c = 11.743(1) A. beta = 113.64(1)°; V = 832.2(2) A3, Z= 2. The strongest lines of the X-ray powder diffraction pattern are: 5.19 (40) (110), 3.53 (40) (3_11), 2.96 (100) (313, 311). 2.80 (50) (020). 2.14 (50) (422, 315, 313), 1.947 (50) (024, 223), 1.657 (40) (407, 333. 331). Type specimen is deposited in the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, wiih registration number 4059/1.
Re: IMA 2010-089 = perrierite-(La)
March 06, 2012 06:54PM
    
I have a structure refinement of a crystal with a very close unit cell:
a = 13.678(3), b = 5.663(1), c = 11.750(2) A, beta = 113.65(3)°; V = 833.7(3) A3
(Material from Günter Blaß as well.)

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