Lanthanite

Abstract: The crystal structure of lanthanite, (La,Ce).(C03k 8H20, a=9.504(4), b= 16.943(6), c=8.937(5) A; space group Pbnb, Z=4, has been determined by Patterson and Fourier methods using 1022 intensities measured with an automatic diffractometer. The hydrogen atoms belonging to three of the four independent water molecules have been located in the difference Fourier map. The least-squares refinement led to a final R index of 0.025. The principal structural feature of lanthanite consists of infinite layers of RE-O coordination polyhedra and CO. 2 - groups. These layers are parallel to the ac plane and are connected to one another only by hydrogen bonds. This feature accounts for the micaceous {01O} cleavage.

Abstract: Lanthanite-(Ce) occurs as a secondary mineral in oxidized copper ore at the Britannia Mine, Snowdoni4 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 t7 oxygens, is (Ce6.rrl-ao.rrNdo.rrSmo.o"Gdo.orYo.oohr.ouCz."rOg.ot'7.96H2O, and the theoretical formula is (Ce,La,Nd)r(CO3)3.8H2O with Ce > La,Nd. Orthorhombic, space goup Pbnb, a:9.482(6), b : 16.938(ll), c : 8.965(3)A,Z:4, D(calc.) :2.79 E/carr for the ideal formula (Ce:La:Nd : 0.83 :0.59 :0.58), D (meas .l : 2.76 g/cmt , V : 144043, a:brc :0.559E :1 :0.5293. Strongest lines in the X-ray powder diffraction pauern are ftlA (I) (hkl)l 8.47(100X020), 4.746(65)l2W),4.462(62NW2),3.255(73N202) and 3.028(65\222\. The mineral is biaxial negative, a 1.532(2), P 1.594(2),y l.6lQ2); orientation X:b, Y:c, Z:a;2V(measJ:60(2)0, 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, HNO.), the mineral reacts with effervescence to yield a gel-like precipitate oflanthanide(Ill) hydroxides.

Abstract: Di represents 'didymium', a name applied to several rare earth elements (REE), including Nd, Pr, etc., which could not be chemically differen­ tiated at that time; accordingly the value of 28.34% represents not only La203, but also (Di203). The true percentage of La203 could therefore be lower than that of Ce203 in this ana­ lysis, and the predominant REE would then be Ce (or Nd) and not La. More recent work has established the existence of a Ce-poor, Nd-rich species of lanthanite from several localities includ­ ing Curitiba, Parana, Brazil (Roberts et al., 1980); Santa Isabel, Sao Paulo, Brazil (Coimbra et al., 1989); Kiringo, Japan (Nagashima et al., 1986), and Bethlehem, Pennsylvania, USA (this work). In order to establish the mineral species name of lanthanite from the type locality Bastnas, a sample from the National Museum of Natural His­ tory of the Smithsonian Institution (catalogue number B10531) was obtained and analysed by energy-dispersive X-ray fluorescence at Sao Paulo, Brazil, and by utilizing both a scanning electron microscope with an attached energy-dis­ persive analyser, and by a wavelength-dispersive electron microprobe at the British Museum (Natural History), London, UK. Ce-poor lantha­ nite, from Bethlehem, Pennsylvania, USA, was also obtained from the Smithsonian Institution (catalogue number R2740) for analysis at the BM(NH) and for comparison with material from Bastnas. Problems with specimen damage by the elec­ tron beam during electron microprobe analysis and the associated analytical difficulties reported by Ansell et al. (1976) and Bevins et al. (1985) were also encountered in this study. However, the proportions of individual REE in the mineral are expected to remain essentially constant during analysis, allowing the mineral species to be named according to the nomenclature procedure of Bay­ liss and Levinson (1988). The data obtained at the BM(NH) on the material from Bastnas are presented in Table 1 (analysis 15), and show the species to be lanthanite-( Ce); and material from Bethlehem (analysis 16) to be lanthanite-(Nd). Si02, CaO andY 203 were the only other elements detected by electron microprobe: Si02 = 0.42% and 0.56%; CaO = 2.08% and 1.22%, and Y203 = 2.27% and 1.80% from Bastnas and Bethlehem respectively. Current rules of nomenclature for rare earth minerals (Bayliss and Levinson, 1988) state that the mineral name be suffixed with the predomi­ nant member of the REE group. Accordingly, examples of lanthanite analyses in the literature have been revised following the recalculation of the atomic percentages of the REE to 100%. These data, and the new data obtained in this study, are presented in Table 1, and show that the lanthanite structure accommodates the light REE (La to Nd). On the basis of the Bayliss and Levinson (1988) revised nomenclature system the lanthanite mineral group constitutes three species:

Abstract: Lanthanite-(Nd) occurs in tuffaceous, altered andesitic agglomerate in the Whitianga quarry, Coromandel Peninsula, New Zealand. The usual platy habit is represented, together with more unusual blocky equant crystals. The former show the new forms {201}, {102} and {111}, and the latter, {111}. ICP–MS analyses show that the distribution of REE (and Ga) is consistent with the formulation (Nd 0.63 La 0.59 Ce 0.35 Pr 0.15 Sm 0.10 Gd 0.069 Y 0.06 Eu 0.03 Dy 0.02 Ga 0.01 ) ∑ 2.04 (CO 3 ) 3 ·8H 2 O; the REE sum of 2.04 is due solely to rounding errors. The find represents the first occurrence of this rare mineral in New Zealand. The mineral formed under comparatively oxidizing conditions. The REE are probably scavenged by warm waters circulating through underlying greywackes of the Manaia Hill Group. We also characterized the lanthanite-(Nd) by X-ray diffraction (powder method) and Raman spectroscopy.