Abstract

Lanthanite-(Ce) occurs as a secondary mineral in oxidized copper ore at the Britannia Mine, Snowdonia, North Wales, U.K. It is found as colorless transparent plates {010} covered by radiating tufts of malachite and is associated with brochantite, posnjakite and chalcoalumite. The analytical formula, based on 17 oxygens, is (Ce0.78La0.55Nd0.55Sm0.09Gd0.05Y0.04)Σ2.06C2.97O9.03 · 7.96H2O, and the theoretical formula is (Ce,La,Nd)2(CO3)3·8H2O with Ce > La,Nd. Orthorhombic, space goup Pbnb, a = 9.482(6), b = 16.938(11), c = 8.965(3)Å, Z = 4, D(calc.) = 2.79 g/cm3 for the ideal formula (Ce:La:Nd = 0.83:0.59:0.58), D (meas.) = 2.76 g/cm3, V = 1440Å3, a:b:c = 0.5598:1:0.5293. Strongest lines in the X-ray powder diffraction pattern are [dÅ (I) (hkl)] 8.47(100)(020), 4.746(65)(200), 4.462(62)(002), 3.255(73)(202) and 3.028(65)(222). The mineral is biaxial negative, α 1.532(2), β 1.594(2), γ 1.616(2); orientation X = b, Y = c, Z = a; 2V(meas.) = 60(2)°, 2V(calc.)=62°, no dispersion observed. The mineral is not fluorescent, and has H = 2.5, a colorless streak, a vitreous luster and is sectile. In dilute mineral acids (HCl, HNO3), the mineral reacts with effervescence to yield a gel-like precipitate of lanthanide(III) hydroxides.

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