The classifi cation of granitic pegmatites was frequently attempted during the past century, with variable degrees of success and applicability. Internal structure, paragenetic relationships, bulk chemical composition, petrogenetic aspects, nature of parent medium, and geochemical features were applied. However, all schemes were marked by contemporary degrees of understanding of these parameters, and most attempts were hindered by ignoring differences in geological environment. Substantial progress was achieved only since the late 1970s. The classifi cation is approached here from two directions, based on but broadened and refi ned from earlier works by Ginsburg and Čern´y. The fi rst concept deals with geological location, leading to division of granitic pegmatites into fi ve classes (abyssal, muscovite, muscovite -rare-element, rare-element, and miarolitic), most of which are subdivided into subclasses with fundamentally different geochemical (and in part geological) characteristics. Further subdivision of most subclasses into types and subtypes follows more subtle differences in geochemical signatures or P-T conditions of solidifi cation, expressed in variable assemblages of accessory minerals. The second approach is petrogenetic, developed for pegmatites derived by igneous differentiation from plutonic parents. Three families are distinguished: an NYF family with progressive accumulation of Nb, Y and F (besides Be, REE, Sc, Ti, Zr, Th and U), fractionated from subaluminous to metaluminous A-and I-type granites that can be generated by a variety of processes involving depleted crust or mantle contributions; a peraluminous LCT family marked by prominent accumulation of Li, Cs and Ta (besides Rb, Be, Sn, B, P and F), derived mainly from S-type granites, less commonly from I-type granites, and a mixed NYF + LCT family of diverse origins, such as contamination of NYF plutons by digestion of undepleted supracrustal rocks.Keywords: classifi cation, granitic pegmatites, geochemistry, mineral assemblage, petrogenesis. SOMMAIREIl y a eu plusieurs tentatives de classifi cation de pegmatites granitiques au cours du siècle dernier, avec un taux de réussite et une applicabilité variables. La structure interne, les relations paragénétiques, la composition chimique globale, les aspects pétrogénétiques, la nature du milieu de croissance, et les caractéristiques géochimiques ont tous été utilisés comme bases de classifi cation. Toutefois, ces schémas ont été limités par le niveau de compréhension de ces paramètres lors de leur application, et par négligeance des différences du milieu géologique. Des progrès substantiels ont seulement été atteints depuis la fi n des années 1970. La classifi cation est abordée ici de deux directions, fondées sur les travaux antérieurs de Ginsburg et Černý, mais affi nés et considérés dans un contexte élargi. Le premier concept porte sur la situation géologique, et mène à cinq classes de pegmatites granitiques: abyssale, à muscovite, à muscovite -éléments rares, à éléments rares et miaro...

A systematic review of the oxide minerals of niobium and tantalum is presented, including varietal names, crystal chemistry, structural features, relationships to other phases and paragenesis of each mineral group, series or species. A separate section deals with oxide minerals that occur exclusively as secondary, low-temperature phases of largely metasomatic origin. Oxide minerals of Sn, Ti and W that carry substantial Nb and Ta are discussed as well. A new crystal chemical classification ofthe oxide minerals ofNb and Ta is presented.Abriefreview is presented of the crystal chemistry ofthe silicates ofNb and Ta, and ofthe silicates ofTi and Zr that exhibit Substitution ofthese elements by Nb and Ta. Paragenetic affiliation of these silicates is reviewed. Miscellaneous minerals of Nb and Ta (borates, phosphates, borosilicates) arealso mentioned.Most of the oxide minerals of Nb and Ta typically occur in granitic rocks of orogenic affiliation, particularly in rare-element granitic pegmatites. However, some ofthese arealso found in, and a few are characteristic of, anorogenic alkaline igneous sequences from carbonatites and gabbros to nepheline syenites and alkaline granites. In contrast, all silicates ofNb (±Ta)-and (Nb,Ta)-bearing titanosilicates and zirconosilicates are related to the anorogenic parageneses.At present, the oxide minerals are the only important sources of Nb and Ta. Niobosilicates, and mainly some of the titanosilicates and zirconosilicates with significant Nb substitution, represent potential ore minerals forthe future. However, no alternate ore minerals seem to be available for extraction of tantalum.Note added in press: Continuing examination ofTa-rich wodginites has revealed the presence of significant quantities of Li, suggestive of a Li4 Ta120 32 component known as a synthetic wodginite-type phase (Gatehouse BM, Leverett P 1972, Lithium triniobate (V), LiNb30 8 ; Cryst Struct Comm 1 :83-86). This development will require modification ofthe wodginite systematics presented here.

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"Allanite" is a poorly defined collection of species belonging to the epidote group. In the past, "allanite" was defined as merely being lanthanon-bearing, but more recently, it is defined as being Ln-dominant at the A2 site. Species of the allanite subgroup include allanite-(Ce), allanite-(La), allanite-(Y), androsite-(La), dissakisite-(Ce), dollaseite-(Ce) and khristovite-(Ce). Lack of recognition of the recommendations of Nickel & Mandarino (1987), and of the relation between members of the subgroup with "allanite" in their species name and those without, has led to a number of errors in naming species and in use of the term "allanite". Ten methods have recently been published describing how the relevant formulae may be calculated. Each is reviewed in conjunction with new observations on the behavior of Si, Cr, V, Mn 2+ and A-site vacancies. This evaluation results in a recommended procedure for the calculation of the formula involving a basis of 6 (M + T) cations and 12(O,F,Cl) + 1(OH). Recalculation of the formulae of published compositions of allanite-subgroup minerals shows that some apparently new species are better interpreted as intermediate solid-solutions between conventional end-members; there are, however, at least five potentially new species awaiting description.

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On a procédé à l'examen des données existantes sur la composition chimique et les propriétés structurales de columbite-tantalite, ferrotapiolite-manganotapiolite, ixiolite, wodginite, rutile tantalifère et niobifère, cassitérite niobo-tantalifère, et du groupe de pyrochlore. La compréhension de la cristallochimie de certaines de ces espèces apparaît quelque peu erronée. La synthèse des observations sur les paragenèses primaires des minéraux de Nb-Ta, caractéristiques des différents types de pegmatites à éléments rares, met en évidence des lacunes considérables lorsque l'on réinterprète les anciennes données partiellement désuètes. Par contre, les données sur les minéraux "exotiques" niobo-tantalifères, récemment découverts, sont complétées par un résumé bien documenté des phénomènes de remplacement et d'altérations tardives. On met en évidence des variations considérables du fractionnement chimique de la columbite-tantalite dans certaines pegmatites et districts pegmatitiques. Afin de comprendre les facteurs qui président à ce fractionnement, il est indispensable d'acquérir les données supplémentaires sur différents types de pegmatites, complétées par des études expérimentales. Les conditions de stabilité chimique et structurale sont mal connues. Leur compréhension nécessite une étude expérimentale détaillée, menée dans des conditions comparables à celles de la cristallisation des bains et fluides pegmatitiques .

Sb 3+ ,As 3+ ) S3 O 12 (O,OH,&) S3 , is a member of the dumortierite group that has been found in pegmatite, or alluvial deposits derived from pegmatite, at three localities: Greenbushes, Western Australia; Voron'i Tundry, Kola Peninsula, Russia; and Szklary, Lower Silesia, Poland. Holtite can contain >30 wt.% Sb 2 O 3 , As 2 O 3 , Ta 2 O 5 , Nb 2 O 5 , and TiO 2 (taken together), but none of these constituents is dominant at a crystallographic site, which raises the question whether this mineral is distinct from dumortierite. The crystal structures of four samples from the three localities have been refined to R 1 = 0.02À0.05. The results show dominantly: Al, Ta, and vacancies at the Al(1) position; Al and vacancies at the Al(2), (3) and (4) sites; Si and vacancies at the Si positions; and Sb, As and vacancies at the Sb sites for both Sb-poor (holtite I) and Sb-rich (holtite II) specimens. Although charge-balance calculations based on our single-crystal structure refinements suggest that essentially no water is present, Fourier transform infrared spectra confirm that some OH is present in the three samples that could be measured. By analogy with dumortierite, the largest peak at 3505À3490 cm À1 is identified with OH at the O(2) and O(7) positions. The single-crystal X-ray refinements and FTIR results suggest the following general formula for holtite: Al 7À[5x+y+z]/3 (Ta,Nb) x & [2x+y+z]/3 BSi 3Ày (Sb,As) y O 18ÀyÀz (OH) z , where x is the total number of pentavalent cations, y is the total amount of Sb + As, and z 4 y is the total amount of OH. Comparison with the electron microprobe compositions suggests the following approximate general formulae Al 5.83 (Ta,Nb) 0.50 & 0.67 BSi 2.50 (Sb,As) 0.50 O 17.00 (OH) 0.50 and Al 5.92 (Ta,Nb) 0.25 & 0.83 BSi 2.00 (Sb,As) 1.00 O 16.00 (OH) 1.00 for holtite I and holtite II respectively. However, the crystal structure refinements do not indicate a fundamental difference in cation ordering that might serve as a criterion for recognizing the two holtites as distinct species, and anion compositions are also not sufficiently different. Moreover, available analyses suggest the possibility of a continuum in the Si/(Sb + As) ratio between holtite I and dumortierite, and at least a partial continuum between holtite I and holtite II. We recommend that use of the terms holtite I and holtite II be discontinued.

Ideal natrotantite has the composition Na2Ta4O11, space group R-3c, a = 6.2092(1), c = 36.619(1) Å, Z = 6. The structure of synthetic natrotantite has been refined by the Rietveld method to Rp = 8.67, Rwp = 9.24, RB = 2.33 % using X-ray powder diffractometer data. The structure consists of layers of (l) edge-sharing NaO7 polyhedra and TaO7 octahedra and (2) edge-sharing TaO7 pentagonal bipyramids, alternating along Z. Natrotantite is topologically identical to, but not isomorphous with Na2Nb4O11 ; the Na2Nb4O11 structure is a monoclinic distortion of the natrotantite structure. The structure is also similar to that of calciotantite from which it differs in its layer (l) topology and in its layer stacking. Natural natrotantites are typically non-stoichiometric ; Na2-xTa4O11-x(OH,F)x is proposed as a more realistic formula for the mineral.