Publication details

Allanite-(Nd), CaNdAl2Fe2+(SiO4)(Si2O7)O(OH), a new mineral from Askagen, Sweden



Year of publication 2012
Type Article in Periodical
Magazine / Source American Mineralogist
MU Faculty or unit

Faculty of Science

Field Geology and mineralogy
Keywords Epidote supergroup; allanite; neodymium; pegmatite; Askagen
Description Allanite-(Nd), ideally CaNdAl2Fe2+(SiO4)(Si2O7)O(OH), the Nd-analog of allanite-(Ce), occurs in the Askagen pegmatite, central Sweden. It forms fine-grained aggregates within altered thalenite-(Y). The other associated minerals include: iimoriite-(Y), keiviite-(Y), allanite-(Y), and tengerite-(Y). Allanite-(Nd) is biaxial (-); with refractive indices alpha = 1.723(5), beta = 1.754(7), gamma = 1.772(5), and measured 2V = 82 degrees(+/- 3 degrees). Larger fragments of allanite-(Nd) are moderately pleochroic (alpha = pale grayish-brown, gamma = grayish-brown); small fragments are colorless. Allanite-(Nd) is monoclinic, space group P2(1)/m, with the following unit-cell parameters: a = 8.8897(5), b = 5.7308(2), c = 10.1010(6) angstrom, beta = 115.166(7)degrees, V = 465.75(4) angstrom(3), Z = 2. The strongest five peaks from the X-ray powder diffraction patterns [d (angstrom)(I)(hkl)] are: 3.51(46)((2) over bar 11), 2.89(100)((1) over bar 13), 2.87(45)(020), 2.70(60)(120), 2.61(60)((3) over bar 11). Allanite-(Nd) has a density of 3.98 g/cm(3), vitreous luster, grayish-brown streak, and the Mohs hardness is ca. 6. It is brittle, with imperfect cleavage, and conchoidal fracture. The Mossbauer spectroscopy revealed Fe3+/Fe-101 ratio of 0.27 in the type sample. The refined empirical formula of the crystal used for the structure determination is: Al(Ca0.957Mn0.043)Sigma(A2)(1.000)(Nd0.337Ca0.154Sm0.131Ce0.125Y0.112Gd0.062Pr0.051DY0.016La0.007Er0.005)(Sigma 1.000) M1(Al0.860Fe0.1403+)(Sigma 1.000)Al-M2(M3)(Fe(0.760)(2+)Al(0.112)Fer(0.070)(3+)Mg(0.058))(Sigma 1.000)(Si3O11.978)-Si-T1,2,3(OH)(1.032). The allanite-(Nd) was approved by CNMNC (IMA 2010-060).
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