AmericanMineralogist, Yolume 70, pages 4ll4I3, 1985 Lanthanite-(Ce),(Ce,La,Nd)z(COs)s .8H2O, a newmineral from Wales,U.K. Rrcunno E. Bnvns Departmentof Geology,National Museumof Wales Cardffi CFI 3NP, Wales,U.K. Gnoncs Rownorn^lrr,r Departmentof Geology,Uniuersity of Keele Keele,ST5 sBG, England,U.K. FnroeRrcr S. SrepHENs Schoolof Chemistry,Macquarie Uniuersity North Ryde, New South Wales2113, Australia SrepnsNTurc@sBr fi.ro PerEn A. Wnrnus Departmentof Chemistry,Uniuersity College PO Box 78, Cardif, CFI IXL, Wales,U.K. Abstract Lanthanite-(Ce)occurs as a secondarymineral in oxidizedcopper ore at the Britannia Mine, Snowdoni4North Wales,U.K. It is found as colorlesstransparent plates {010} coveredby radiatingtufts of malachiteand is associatedwith 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)3.8H2Owith 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/carrfor the idealformula (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. Strongestlines 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 nega- tive,a 1.532(2),P 1.594(2),yl.6lQ2); orientationX:b, Y:c, Z:a;2V(measJ:60(2)0, 2V(calc.)=62",no dispersionobserved. The mineralis not fluorescent,and has H:2.5, a colorlessstreak, a vitreous luster and is sectile.In dilute mineral acids (HCl, HNO.), the mineral reactswith effervescenceto yield a gel-likeprecipitate oflanthanide(Ill) hydroxides. Introduction In the courseof our studieson the geologyand mineral- Lanthanite, the lanthanum end-memberof the seriesof ogy of the Britannia Mine, North Wales,U.K., (National minerals with the general stoichiometry (RE)r(CO3)3' Grid Ref. SH 615 547),we found clear platy crystals in 8HrO, was first describedby Berzelius(1825). Its general oxidized copper ore. This material proved to be the new composition was determinedby Blake (1853)and Genth mineral lanthanite-(Ce),the cerium-predominantmember (1857).The presenceof other lanthanides("didymium") in of the lanthanitegroup, which is describedbelow. The min- the material from Bethlehem,Pennsylvania, U.S.A., was eral and its namehave been approved, prior to publication, noted. It is a rare mineral species,but has been noted to by the Commissionon New Minerals and Mineral Names, occur sparingly at a number of localities (Saebo,1961). IMA. Lanthanite-(Ce)is namedin ac'cordancewith the ac- Lanthanite-(Nd)(Roberts et al., 1980)was found recentlyin ceptedrare earth minerals nomenclature(Levinson, 1966). a silty arenaceousclay at Curitiba, Paran6,Brazil; Nd and Type material (National Museum of Wales specimen La were the main rare earthspresent, together with minor number NMW 84.6G.M1)has been depositedin the col- Pr, Sm, Gd, Eu, Dy, Y and Ce. lection of the National Museum of Waks and is available for further study. Other material has been depositedwith r Presentaddress: Conservation Department, UMIST, PO Box the British Museum(Natural History), the SmithsonianIn- 88,Manchester, M60 lQD, England,U.K. stitution and Museede Mineralogie,Paris. 0003-o04x/85/030,4I 1$02.00 4ll 4r2 BEVINS ET AL.: LANTHANITE-(Ce) Occurrence and associations Table 1. Analytical data for lanthanite{Ce) Lanthanite-(Ce)was found in the secondlowest accessi- ble level of the Britannia Mine. Well-crystallizedplates (Fig. 1),up to 5 x 5 x 0.5 mm, occur on the walls and back of the adit, and are coatedon {010} by spheresof acicular Ce 17.60 ,"r03 20.61 radiating malachite. Associatedminerals are brochantite, 12.31 taz03 14.44 posnjakite and rarely chalcoalumite.This whole assem- Nd 12.67 Ndzo3 14. z8 blage is sometimesfound coated with a glaze of ferric oxyhydroxides. Sr203 2.50 Lanthanite-(Ce),as well as its asSociates,is obviously of Gd 1.33 Gd203 1.53 secondaryorigin and has crystallizeddue to rare earth- u.50 'ro3 o'l\ bearing groundwaters percolating through the old mine -h c0- 21.0 coz 2r.0 workings. The rare earths may have been leached from b allanite which has beenidentified in the acid pyroclasticsof H-0 23.0 Hzo 23.0 c the SnowdonVolcanic Group (G. Hendry, pers.comm.). In Total 98.6 the immediatemine area,high concentrationsof rare earth elements are present in the rhyolitic intrusions of the a Snowdon Volcanic Group. Theseintrusions contain La in Rare-ea.ths recalculated to oxides. Rare_ percents average of five the range 60-100 ppm, Ce 140-200ppm and Nd 70-120 earth weight are the el ectron microprobe anal yses. ppm (T.K. Ball,pers. comm.). b Alro th" average of five analyses' c Physical and optical properties The empirical formula based on t7 oxygens is Lanthanite-(Ce)is colorless,transparent and platy {010}. {ctg.7BL"o. 55Nd0. 55sto. o9cdo. o5Yo. oq)rz. o6cz. 97 No other forms were observed,all of the platesso far seen 09.8.7.96Hro. terminating with ragged edges.It has a white streak, a vitreousluster and is not fluorescent.The hardnessis about 2.5 and the plates are sectile. Cleavage {010} is well- developed.The mineral dissolvesin dilute mineral acids (HCl, HNO3) with effervescenceto yield a gel-like precipi- tate of lanthanide(Ill) hydroxides.Density was determined by flotation of hand-picked crystals; the value of 2.76 g/cm3 comparesfavorably with the calculateddensity of 2.79 glcm3based on the theoreticalformula withZ : 4. The mineral is biaxial negativewith measuredrefractive indices a r.532(2),P t.594(2),y r.616(2\(,1:589 nm). 2ll(meas.)was 60(2)",the calculated value being 62". No dispersionwas observed.The orientation is X : b, Y : c, Z : a. The compatibility (1 - (Ke/K") : -0.010) is su- perior based on the Gladstone-Dale calculation. The physicaland optical valuesare closeto thoseof Larsenand Berman (1934)and Saebo(1961) for lanthanite,and those of Robertset al. (1980)for lanthanite-(Nd). Chemical composition Electron microprobe analyseswere carried out at the University of Manchesterusing a Cameca(Camebax) in- strument operating at 15 kV and with a specimencurrent of 3.5 x l0-E A in the energydispersive mode. Analytical graderare earth oxides(CerOr, LarO3, Nd2O3, SmrO., Gd2O3and YrO.) wereused as standardsand the X-ray lines usedwere La with correctionsmade for interferingLB lines.CO, was determinedusing a TechniconCHN analy- ser and water of hydration analyseswere performed ther- mogravimetrically using a Stanton Redcroft TG 750 pre- Fig. 1. (upper) Scanning electron photomicrograph of temperature-programmedbalance. Analytical data are lanthanite{Ce) encrusted with malachite and (lower) an annotated sented in Table 1. The empirical formula based on 17 sketch of the same area. Lan : lanthanite-(Ce) and Ma- oxygen atoms is (Ceo.rrl-ao.rrNdo.rrSmo.onGdo.o, I : malachite. Yooohr.ouCz.rrOr.o..7.96H2O.The massdeflciency in the BEVINS ET AL: LANTHANITEICe\ 4r3 Table 2. Unit cell data for lanthanitegroup minerals lanthanite-(Ce) is (Ce,La,Nd)r(CO3)3.8H2O with Ce > La,Nd, and the Ce:La:Nd ratio usedto calculatethe densityof the mineralis 0.83:0.59:0.58. ,o. a (A) 9.482 (5 ) 9. 50tr(4) 9.476(4) X-ray data _o. b (A) r6.938(il) 16.943(6) 16 940(8) Single-crystalprecession studies of orientedcrystals indi- o. pa- c (A) 8.965(3) 8.937(5) 8.942(4) cated orthorhombic symmetry,and measuredunit cell rameters are a : 9.4846), b : 16.938(11),c : 8.965(3)A. a(meas.) (g/cn3) 2.16 2.8r Quoted errors are derived from multiple measurementsof a(calc.)(s/cml) 2.79 2.78 2.82 precessionphotographic data, using MoKa radiation. V : z\ 4 4 l44OAtandZ:4; a:b:c: 0.5598:1:O.5293. Systematic ab- qn-.A ^r^"^ Dhhh sencesin the reflexionrecord are Okl (k:2n + l), hk0 !=!= Pbnb Pbnb (k : 2n + 1) and h0l (h + I : 2n * 1) which uniquely define the space group Pbnb (a non-standard setting of spacegroup Pccn).These data are entirely consistentwith l. Lanthanite-(Ce); this study, those reported by Dal Negro et al. (1977) on a natural Lanthanite; Bastnes, Sweden; Dal Negro * al. (1977). sample of lanthanite (lanthanite-(La)) from Bastnds, 1 Lanthanite-(Nd); Paran5, Brazil; Roberrs et al. (1980). Sweden,and by Roberts et al. (1980)on lanthanite-(Nd) from Curitiba, Paran6, Brazil. Single-crystaldata for all three minerals are compared in Table 2. The strongest analyticalresults may be attributed to sampledeterioration X-ray lines in the powder diflraction pattern, listed in during preparation and probe analysis.This was also ob- Table 3, are ldA g](hkl)l 8.47(100x020),4.746(6s){2o0), servedduring microprobe analysesof lanthanite-(Nd),but 4.462(62)(002),3.2ss(73){202) and 3.o28(65N222).The in that case sample deterioration was much more pro- powder data are virtually identical to those tabulated by nounced (Ansell et al., 19761.The ideal formula for Robertset al. (1980)for lanthanite-(Nd).Obviously, quanti- tative chemicalanalyses are necessaryfor a reliable distinc- tion betweenmembers of the lanthanitegroup. Table 3. X-ray powderdata for lanthanite-(Ce) Acknowledgments o o We wishto thankProfessors Mackenzie and Zussman, Depart- r/r d A obs. ^ dAcalc. hkl mentof Geology,Manchester University for the useof electron microprobefacilities, and D. Plant for preparingthe rare earth Roberts considerablyimproved the manuscript r00 8. lr7 8.\69 020 standards.A. C. with a thorough review.The technicalassistance of Mike Lambert \.746 \.7\1 200 (NMW) is alsoappreciated.