- © 2012 Mineralogical Society of America
Allanite-(Nd), ideally CaNdAl2Fe2+(SiO4)(Si2O7)O(OH), the Nd-analog of allanite-(Ce), occurs in the Åskagen pegmatite, central Sweden. It forms fine-grained aggregates within altered thalénite-(Y). The other associated minerals include: iimoriite-(Y), keiviite-(Y), allanite-(Y), and tengerite-(Y). Allanite-(Nd) is biaxial (−); with refractive indices α = 1.723(5), β = 1.754(7), γ = 1.772(5), and measured 2V = 82°(±3°). Larger fragments of allanite-(Nd) are moderately pleochroic (α = pale grayish-brown, γ = grayish-brown); small fragments are colorless. Allanite-(Nd) is monoclinic, space group P21/m, with the following unit-cell parameters: a = 8.8897(5), b = 5.7308(2), c = 10.1010(6) Å, β = 115.166(7)°, V = 465.75(4) Å3, Z = 2. The strongest five peaks from the X-ray powder diffraction patterns [d (Å)(I)(hkl)] are: 3.51(46)(2̄11), 2.89(100)(1̄13), 2.87(45)(020), 2.70(60)(120), 2.61(60)(3̄11). Allanite-(Nd) has a density of 3.98 g/cm3, vitreous luster, grayish-brown streak, and the Mohs hardness is ca. 6. It is brittle, with imperfect cleavage, and conchoidal fracture. The Mössbauer spectroscopy revealed Fe3+/Fetot ratio of 0.27 in the type sample. The refined empirical formula of the crystal used for the structure determination is:
The allanite-(Nd) was approved by CNMNC (IMA 2010-060).