Nonmetamict nioboeschynite-(Ce) from Alaska Available to Purchase

Crystals of essentially nonmetamict nioboeschynite-(Ce), a complex oxide with the general formula AB₂O₆, were identified in an alluvial concentrate from the Tofty tin belt in central Alaska. The mineral grains are mostly sand-size (0.2 to 1.5 mm), red-brown to dark brown, generally tabular, slender to stubby striated prisms, Crystal parameters of this rare orthorhombic mineral are: a = 5.396, b = 11.085, c = 7.585 Å, V = 453.7 ų, space group = Pbnm, Z = 4; D = 5.04 g/cm³; RI: α = 2 27; β = 2.32, γ = 2.34, (-) 2V (av.)= 84.6°, γ, α and β are parallel to crystallographic a-, b-, and c-directions, respectively; prominent d values (and relative intensities) = 2.98 10, 3.05 7, 3.13 4, 5.53 2, 3.44 2, 2.82 2, 2.70 2, 2.04 2, 1.72 2, and 1.61 2. Spectrochemical analysis shows (in percent): CaO 4.52, FeO 1.09, La₂O₃ 4.9, Ce₂O₃ 15.8, Pr₂O₃ 1.9, Nd₂O₃ 5.6, Y₂O₃ 0.18, ThO₂ 1.33, U₃O₈ 0.01, SiO₂ 3.51, Nb₂O₃ 47.0, TiO₂ 20.2, ∑ = 106; minor elements (in parts per million) include Ba 2000, Be 10, Cr 300, Cu 30, Mg < 10, Mn 40, Pb 100, Sb 50, and Ta < 1000. The structural formula computed from the analysisis (Ca_0.27Fe_0.05La_0.10Ce_0.32Pr_0.04Nd_0.11Y_0.01Th_0.02)_0.92(Nb_1.17Ti_0.83)_2.00O_5.78

Nonmetamict eschynite is rare; only five crystalline to partly metamict specimens were described in the literature. The physical, chemical, and X-ray data of Alaskan eschynite are compared with data for such eschynites from the Ural Mountains in the USSR, and northern China.