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The columbite supergroup is established. It includes five mineral groups (ixiolite, wolframite, samarskite, columbite and wodginite) and one ungrouped species (lithiotantite). The criteria for a mineral to belong to the columbite supergroup are: the general stoichiometry M O2; the crystal structure based on the hexagonal close packing (hcp) of anions (or close to it); the six-fold coordination number of M -type cations (augmented to eight-fold in the case of slight distortion of hcp); and the presence of zig-zag chains of edge-sharing M -centred polyhedra. The ixiolite-type structure is considered as an aristotype with the space group Pbcn , the smallest unit cell volume, and the basic vectors a0 , b0 and c0. Based on the multiplying of the ixiolite-type unit cell the following derivatives are distinguished: ixiolite type [ixiolite-group minerals; a = a0, b = b0 and c = c0 ; space group Pbcn ; the members are ixiolite-(Mn2+), ixiolite-(Fe2+), scrutinyite, seifertite and srilankite]; wolframite type [wolframite-group minerals, ordered analogues of the ixiolite type with a = a0, b = b0 and c = c0 ; P 2/ c ; the members are ferberite, hübnerite, huanzalaite, sanmartinite, heftetjernite, nioboheftetjernite, rossovskyite and riesite]; samarskite type [samarskite-group minerals; a = 2 a0 , b = b0 and c = c0 ; P 2/ c ; the members are samarskite-(Y), ekebergite and shakhdaraite-(Y)]; columbite type [columbite-group minerals; a = 3 a0, b = b0 and c = c0 ; Pbcn ; the members are columbite-(Fe), columbite-(Mn), columbite-(Mg), tantalite-(Fe), tantalite-(Mn), tantalite-(Mg), fersmite, euxenite-(Y), tanteuxenite-(Y) and uranopolycrase]; and wodginite type [wodginite-group minerals; a = 2 a0, b = 2 b0 and c = c0 ; C 2/ c ; the members are wodginite, ferrowodginite, titanowodginite, ferrotitanowodginite, tantalowodginite, lithiowodginite and achalaite]. Samarskite-(Yb), ishikawaite and calciosamarskite are insufficiently studied, tentatively considered as possible members of the samarskite supergroup. Qitianlingite, yttrocolumbite-(Y), yttrotantalite-(Y) and yttrocrasite-(Y) are questionable and need further studies. Polycrase-(Y) is discredited as identical to euxenite-(Y). Ixiolite has been renamed as ixiolite-(Mn2+), with the end-member formula (Ta2/3Mn2+1/3)O2. Ta- and Nb-dominant analogues of ixiolite with different schemes of charge balancing have the end-member formulae (M 15+0.5 M 23+0.5)O2, M 15+2/3 M 22+1/3)O2, M 15+0.75 M 2+0.25)O2 or M 15+0.8□0.2)O2 and the root name 'ixiolite' (for M 1 = Ta) or 'nioboixiolite' (for M 1 = Nb). [ABSTRACT FROM AUTHOR]

The crystal structure of calcioaravaipaite, Pb[Ca.sub.2]Al[(F,OH).sub.9], was initially solved by direct methods in the monoclinic space group A2/m (R = 12.4%). Further study demonstrated the OD nature of the structure, and showed that the crystal was twinned. The structure was solved in the triclinic space group C[bar]1, a = 7.722(3), b = 7.516(3), c = 12.206(4)/[Angstrom], [alpha] = 98.86(1), [beta] = 96.91(1), [gamma] = 90.00(1)[degrees], V = 694.8(3) [[Angstrom].sup.3], Z = 4, yielding R = 5.1% for 1420 reflections with [F.sub.0] > 4[sigma]([F.sub.0]). Calcioaravaipaite belongs to a family of order-disorder (OD) structures formed by equivalent layers of symmetry C2/m. Two maximum-degree-of-order (MDO) polytypes are possible. MDO1 results from a regular alternation of stacking operators [2.sub.1/2] and [2.sub.-1/2] and yields a monoclinic structure with C2/c, a = 7.72, b = 7.52, c = 24.12 [Angstrom], [beta] = 96.99[degrees]. MDO2 results from the sequence [2.sub.1/2]/[2.sub.1/2]/[2.sub.1/2]/ ... and yields a triclinic structure with a = 7.72, b = 7.52, c = 12.21 [Angstrom], [alpha] = 98.86, [beta] = 96.91, [gamma] = 90.00[degrees]. The structure of calcioaravaipaite is comprised of two kinds of alternating polyhedral slabs parallel to (001). Slab 1 consists of a fluorite-like double layer of edge-sharing (Ca[F.sub.8]) distorted cubes and slab 2 is a composite of face- and edge-sharing (Pb[F.sub.12]) polyhedra and outlying (Al[F.sub.6]) octahedra, the latter sharing faces and edges with the (Pb[F.sub.12]) polyhedra, but no elements with one another. Aravaipaite and calcioaravaipaite share a common fluorite-type layer; however, in aravaipaite the presence of [Pb.sup.2+] rather than [Ca.sup.2+] in this layer results in slabs of strikingly different polyhedral configuration.

Scandiobabingtonite, ideally [Ca.sub.2]([Fe.sup.2+], Mn)Sc[Si.sub.5][O.sub.14](OH) is the scandium analogue of babingtonite; it was found in a pegmatitic cavity of the Baveno granite associated with orthoclase, albite, muscovite, stilbite, and fluorite. Its optics are biaxial (+) with 2V = 64(2) [degrees], [Alpha] = 1.686(2), [Beta] = 1.694(3), [Gamma] = 1.709(2). [D.sub.meas] = 3.24(5) g/[cm.sup.3], [D.sub.calc] = 3.24 g/[cm.sup.3], and Z = 2. Scandiobabingtonite is colorless or pale gray-green, transparent, with vitreous luster. It occurs as submillimeter sized, short, tabular crystals, slightly elongated on [001], and characterized by the association of forms {010}, {001}, {110}, [Mathematical Expression Omitted], and {101}. It occurs also as a thin rim encrusting small crystals of babingtonite. The strongest lines in the X-ray powder pattern are at 2.969 (S), 2.895 (S), 3.14 (mS), and 2.755 (mS) A. The mineral is triclinic, space group PT, with a = 7.536(2), b = 11.734(2), c = 6.748(2) A, [Alpha] = 91.70(2), [Beta] = 93.86(2), [Gamma] = 104.53(2) [degrees] . Scandiobabingtonite is isostructural with babingtonite, with Sc replacing [Fe.sup.3-] in six-fold coordination, but no substitution of [Fe.sup.2+] by Sc takes place. Due to the lack of a suitably large crystal of the new species, such a replacement has been confirmed by refining the crystal structure of a Sc-rich babingtonite (final R = 0.047) using single-crystal X-ray diffraction (XRD) data.