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Lanthanite
Lanthanites are a group of isostructural rare earth element (REE) carbonate minerals. This group comprises the minerals lanthanite-(La),〔Haidinger W (1845) Zweite Klasse: Geogenide. II. Ordnung. Baryte. III. Cerebaryt. Lanthanit., in Handbuch der Bestimmenden Mineralogie, Bei Braumüller and Seidel (Wien) 499-506.〕〔Nickel E H, Mandarino J A (1987) Procedures involving the IMA Commission on New Minerals and Mineral Names and guidelines on mineral nomenclature, American Mineralogist 72, 1031-1042.〕 lanthanite-(Ce),〔Bevins R E, Rowbotham G, Stephens F S, Turgoose S, Williams P A (1985) Lanthanite-(Ce), (Ce,La,Nd)2(CO3)3·8H2O, a new mineral from Wales, U.K.. American Mineralogist 70, 411-413.〕 and lanthanite-(Nd).〔Roberts A C, Chao G Y, Cesbron F (1980) Lanthanite-(Nd), a new mineral from Curitiba, Parana, Brazil, Geological Survey of Canada Paper 80-1C, 141-142.〕 This mineral group has the general chemical formula of (''REE'')2(CO3)3·8(H2O). Lanthanites include La, Ce, and Nd as major elements and often contain subordinate amounts of other REEs including praseodymium (Pr), samarium (Sm), europium (Eu) and dysprosium (Dy).〔The Canadian Mineralogist 45 (2007) 1389-1396.〕 The lanthanite crystal structure consists of layers of 10-fold coordinated REE-oxygen (O) polyhedra and carbonate (CO3=) groups connected by hydrogen bonds to interlayer water molecules, forming a highly hydrated structure.〔Morrison, S. M., Andrade, M. B., Wenz, M. D., Domanik, K. J., & Downs, R. T. (2013). Lanthanite-(Nd), Nd2 (CO3) 3.8 H2O. Acta Crystallographica Section E: Structure Reports Online, 69(3), i15-i16. 〕
==Origin and formation==
Lanthanites are frequently found as secondary minerals formed by the weathering of other minerals and occur as scales or tabular crystals. Originally identified at Bastnäs, Sweden,〔Berzelius, J. (1825). Taschenbuch für die gesamte Mineralogie mit Hinsicht auf die neuesten Entdeckungen, 19, 193-218.〕 they have subsequently been found in New Zealand,〔Graham, I.T., Pogson, R.E.,Colchester, D.M., Hergt, J. Martin, R. & Williams, P.A. (2007): Pink Lanthanite-(Nd) from Whitianga Quarry, Coromandel Peninsula, New Zealand. Canadian Mineralogist. 45: 1389-1396〕 Japan,〔American Mineralogist: 71(7-8): 1028-1033.〕 Madagascar,〔Behier, J. (1960): Contribution á la mineralogie de Madagascar. Annales Géologiques de Madagascar XXIX, Tananarive, p 18〕 Wales,〔Amer.Min.(1985) 70, 411-413〕 China,〔Zhang Peishan, Yang Zhuming, Tao Kejie, and Yang Xueming (1996): "Mineralogy and Geology of Rare Earths in China", Science Press (Beijing), 226 pp.〕 France, 〔Remy, P., Gatel, P., Meisser, N. (2014): Indice à terres rares de Mosset (Pyrénées-Orientales). Le Cahier des Micromonteurs, 1-2014, 3-17.〕 Germany, 〔Gröbner, J., Hajek, W., Junker, R. & Nikoleizig, J. (2011): Neue Mineralschätze des Harzes. Papierflieger Verlag GmbH, Clausthal-Zellerfeld, Germany, 127 pp.〕 Greenland,〔Petersen, O. V. and Secher, K. (1993): The minerals of Greenland, The Mineralogical Record, Vol. 24(2), 1-65〕 Finland,〔Sotka, P. 1984. Juuka, Panjavaara: Ce-La-Sr-mineraalien esiintyminen karbonaattijuonissa. Outokumpu OY raportti 070/4312 08A/PMS/1984.〕 Canada,〔HORVÁTH, L. & PFENNINGER-HORVÁTH, E. (2000) I minerali di Mont-Saint-Hilaire (Québec, Canada) Rivista Mineralogica Italiana, XXIV, 140-202.〕 Austria,〔G. Niedermayr, I. Praetzel: Mineralien Kärntens, 1995.〕 Romania,〔Szakáll, S. & Kristály, F., Eds. (2010): Mineralogy of Székelyland, Eastern Transylvania, Romania. Csík County Nature and Conservation Society, Miercurea-Ciuc, Romania, 321 pp.〕 Norway,〔Sæbø, P.Chr. (1961): Contribution to the mineralogy of Norway. No.11. On lanthanite in Norway. Norsk Geologisk Tidsskrift. 41: 311-317〕 Brazil,〔Roberts, A.C., G.Y. Chao, and F. Cesbron (1980) Lanthanite-(Nd), a new mineral from Curitiba, Paran ́a, Brazil. Geol. Surv. Canada, Paper 80-1C, 141–142.〕 and the United States.〔"Minerals of Colorado, updated & revised", p. 14, by Eckel, Edwin B., 1997.〕
Recently, a different mechanism of formation of lanthanites was discovered: Lanthanites also can form via a highly hydrated, nanoparticulate and poorly ordered carbonate precursor.〔Rodriguez-Blanco, J.D., Vallina, B., Blanco, J.A. and Benning, L.G. (2014) The role of REE3+ in the crystallization of lanthanites. Mineralogical Magazine, 78, 1373–1380. (DOI: 10.1180/minmag.2014.078.6.03 )〕 The lifetime of this rare-earth bearing precursor as well as the kinetics of crystallization of the various REE-lanthanites are dependent on the specific trivalent rare-earth ion involved in the reaction. The times needed for lanthanites to fully crystallize increase linearly with the ionic potential of the trivalent rare-earth ion (La3+, Ce3+, Pr3+, Nd3+) present in their structure. The differences in these ion sizes and ionic potential as well as differences in dehydration energy of the trivalent rare-earth ions control the lifetime of the poorly ordered precursor and thus also the crystallization kinetics of the lanthanites. Furthermore, they also affect the structural characteristics (e.g. unit-cell dimensions and standard shape) of the crystals.
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