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Nous avons resolu la structure cristalline de l'ilimaussite-(Ce), (Ba,Na) 1 0 K 3 Na 4 . 5 Ce 5 (Nb,Ti) 6 [Si 1 2 O 3 6 ][Si 9 O 1 8 (O,OH) 2 4 ]O 6 , provenant de la localite-type, le complexe alcalin d'Ilimaussaq, dans le sud du Groenland, et nous l'avons affine jusqu'a un residu R de 0.11 pour 1663 reflexions observees, prelevees sur un cristal de bien pietre qualite [a 10.770(3), c 61.05(2)A; groupe spatial R32, Z = 3; rayonnement MoKα; diffractometre Nonius Kappa CCD]. La structure est faite de trois paires de feuillets silicates. En intercalation entre ces feuillets (001 ) sont: des prismes trigonaux CeO 6 et des cations Na (feuillet A ), des octaedres NbO 6 , Ba, et K (feuillet O), et des prismes trigonaux CeO 6 (feuillet A'). Les feuillets sont empiles selon la sequence AOA'O. Les sites tetraedriques du feuillet A' ne seraient que 50% remplis par le Si, et par consequent, il y a un desordre dans les atomes d'oxygene a la base. En tout, le rapport de (Si + Al) aux autres cations est egal a 0.8 environ. Dans la structure semblable d'un analogue a dominance de Ti de l'ilimaussite-(Ce), a comparer a la diversilite-(Ce), les memes sites ont ete decrits avec un taux d'occupation de 1/3; dans ce cas, le rapport de (Si + Al) aux autres cations est egal a 1.2 environ. Nous presentons de nouvelles donnees chimiques decrivant la diversilite-(Ce), dans laquelle le rapport de (Si + Al) aux autres cations est egal a 0.9 environ. Il est possible qu'il y ait une famille de phases de type "ilimaussite" ayant des compositions dans l'intervalle 21 < Si ≤ 24 apfu, avec un polytypisme lie au desordre dans le feuillet A'.

Seidite-(Ce), Na 4 (Ce,Sr) 2 {Ti(OH) 2 (Si 8 O 1 8 )}(O,OH,F) 4 5H 2 O, is a titanosilicate recently discovered in the Yubileynaya pegmatite at Mount Karnasurt, Lovozero alkaline massif, Kola Peninsula, Russia. Grains consist of disordered [010] fibers; no single crystals suitable for X-ray diffraction have found. On the basis of chemical composition, electron and X-ray powder-diffraction data, and by comparison with the structure of miserite, KCa 5 (Si 2 O 7 )(Si 6 O 1 5 )(OH)F, a structure model for seidite-(Ce) has been developed in space group C2/c [a 24.61(5), b 7.23(1), c 14.53(3) A, β 94.6(3)°, Z=4]. In the crystal structure of seidite-(Ce), the isolated eight-membered silicate channels of miserite are condensed into (100) layers that are connected by isolated TiO 6 octahedra to form a framework. In the chemical formula, the composition of the framework is shown within braces. There are two types of channels involving TiO 6 octahedra and SiO 4 tetrahedra: one is eight-membered and is parallel to the silicate channel along [010]; the other is ten-membered and extends along [001]. Cations other than Si and Ti occur within the channels, together with H 2 O groups and OH,F anions. The Na cations are easily exchanged for Tl, K, Rb, Cs and Ba, indicating the microporous behavior of the seidite-(Ce) structure. We describe the mero-plesiotype modular aspects of seidite-(Ce) and related compounds belonging to the rhodesite group. comportement microporeux par la structure de la seidite-(Ce). Nous decrivons les aspects modulaires de type mero-plesiotype de la seidite-(Ce) et des composes semblables faisant partie du groupe de la rhodesite.

Tsepinite- Ca, ideally (Ca,K,Na, h )2(Ti,Nb)2(Si4O12)(OH,O)2·4H2O (Z = 4), is a new mineral species of the labuntsovite group (vuoriyarvite subgroup) found in the abandoned Lovchorrite mine, Hackman Valley, Yukspor Mountain, Khibiny massif, Kola Peninsula, Russia. It occurs in the hydrothermally altered zone of a large aegirine- nepheline- potassic feldspar pegmatite and is associated mainly with microcline, aegirine, natrolite, kentbrooksite, kupletskite, Mn-rich lamprophyllite, fluorapatite, catapleiite, ancylite- (Ce), ancylite- (La), fluorapo- phyllite, leucophanite, chabazite- Ca. The new mineral is late hydrothermal and oc- curs in cavities after leaching of rinkite, the probable source of Ti, Nb and Ca. Tse- pinite- Ca forms coarse long-prismatic to needle-shaped and usually split crystals which are transparent, colourless to white and pale brownish, up to 0.2 ´0.6´5mm in size and form aggregates up to 1cm in size. The streak is white and the lustre is vitreous. Tsepinite- Ca is brittle, shows uneven fracture and no cleavage. Its Mohs' hardness is 5; Dmeas. = 2.73(1), Dcalc. = 2.72g/cm 3 . Biaxial (+), 2Vmeas. = 30 ± 10ƒ, 2Vcalc. = 36ƒ; a = 1.666(2), b = 1.676(2), g = 1.780(4). Dispersion is very weak: r < n. Non-pleochroic; the orientation is Y = b. The strongest IR bands (cm -1 ) are at 3260, 1103, 946, 673, 455. Electron microprobe analysis (H 2O by TGA) gave: Na 2O

The crystal structure of vlasovite obtained from the Kipawa alkaline complex in Quebec is refined to RF = 0.053 for 1515 unique reflections with |F| > 4σ(F). The parameters of the monoclinic unit are as follows: a = 11.063(8) A, b = 10.15(1) A, c = 8.60(1) A, β = 100.3(1)°, space group C2/c, and Z = 4. The X-ray diffraction, electron microprobe, and IR spectroscopic data indicate that, under X-ray radiation, the specimen suffers radiation damage, which is accompanied by a partial removal of Na atoms, incorporation of H2O molecules into the structure, and, possibly, a change in the configuration of the (Si,O) framework.

Gjerdingenite-Fe occurs as yellow prisms or laths up to 1 mm long in miarolitic cavities of a sodic granite (“ekerite”) at Gjerdingselva, Lunner, Oppland, Oslo Region, Norway. The simplified formula is K 2 [(H 2 O) 2 (Fe,Mn)][(Nb,Ti) 4 (Si 4 O 12 ) 2 (OH,O) 4 ]·4H 2 O, i.e. , the mineral is an analogue of those with root name kuzmenkoite, which have Ti > Nb. The mineral is monoclinic, C 2/ m , with a 14.529(2), b 13.943(2), c 7.837(2) A, β 117.61(1)°, V 1406.8(9) A 3 , Z = 2. The crystal structure was refined to R = 0.054 on the basis of 1677 observed reflections; twinning on {001} simulates an orthorhombic F -centered lattice. The partitioning of cations and H 2 O molecules in the sites B , B ′, C (occupying channels of the zeolite-like structure) is discussed; for the refined crystal, the following crystal-chemical formula is established by comparison of chemical and structure-refinement data: {[K 1.20 Na 0.72 (H 2 O) 2.08 ] ∑4 [K 2.08 (H 2 O) 1.92 ] ∑4 }[(H 2 O) 3.40 K 0.56 Ca 0.04 ] ∑4 (Fe 0.95 Mn 0.75 □ 0.30 ) ∑2 (Nb 4.30 Ti 3.45 Fe 0.20 Zr 0.05 ) ∑8 (Si 15.90 Al 0.10 ) ∑16 O 48 [(OH) 4.16 O 3.84 ] ∑8 ·4H 2 O ( Z = 1). The strongest six reflections of the powder pattern [ d obs in A( I )( hkl )] are: 6.92(80)(020,001), 6.42(50)(200,201), 4.94(70)(021), 3.225(100)(421,400,402), 3.114(80)(041,022), and 2.512(50)(441,401,403). The mineral is optically biaxial (+) with α 1.6676(2), β 1.7001(4), γ 1.794(1); 2 V meas = 58.5(2.3)°, 2 V calc = 63.71(1)°. The Mohs hardness is about 5; D meas = 2.82(2), D calc = 2.830 g/cm 3 . The pseudo-orthorhombic crystals are flattened on {001} and elongate along [010]. Five crystal forms were observed: {100}, {010} (subordinate), {001}, {201}, and {021}.

Bornemanite is a rare alkali titanosilicate occurring in the natrolite zone of the Yubileynaya hyperagpaitic pegmatite, on Karnasurt Mountain, in the Lovozero massif, Kola Peninsula, Russia. The mineral is light yellow, lamellar (001) and elongate [010]. No single crystals suitable for X-ray crystallography are available. New electron-microprobe chemical analyses, selected area electron diffraction (SAED) and X-ray powder diffraction show that bornemanite, BaNa 3{(Na,Ti)4[(Ti,Nb)2O2Si4O14] (F,OH)2}PO4, is monoclinic I11b, a 5.498(4), b 7.120(6), c 47.95(4) A, � 88.4(1)°; Z = 4. By comparison with structural and chemical data for titanosilicates based on a bafertisite-like layer (heterophyllosilicates), a model of the structure of bornem anite has been obtained. This model has been refined by the distance least-squares technique (DLS program) and tested against calculated powder-diffraction and SAED patterns. The structure of bornemanite can be described as a [001] stacking of heterophyllosilicate layers, where lomonosovite and seidozerite contents alternate in the interlayer spaces. Thus this structur e is the first documented case of a heterophyllosilicate based on modules of two other structures belonging to the same modular series, i.e., the mero-plesiotype bafertisite series. The lomonosovite–seidozerite polysomatic series is defined. In contrast to the original description, bornemanite is considered monoclinic and not orthorhombic, and lacks one cation per formula unit (mainly Na). Possible leaching of alkalis and the solid-state oriented transformation lomonosovite → bornemanite are discussed.

Several structural families reported in this book can be described by using concepts of modular crystallography (Thompson 1978; Veblen 1991; Merlino 1997; Ferraris et al. 2004). This chapter presents three groups of microporous minerals emphasizing the modular aspects of their crystal structures and the role that modularity plays in correlating different structures as well as structure and properties, namely aspects aimed at an engineering of microporous materials (cf. Rocha and Lin 2005). The description of a crystal structure as an edifice consisting of complex building modules that occur also in other structures implicitly leads to identify features that are common to a group of compounds. This kind of group can often be expressed as a series of structures that are collinear in composition and cell parameters, information that may be crucial to model unknown structures related to the series, as illustrated by some examples in this chapter. Biopyriboles (Fig. 1⇓) represent a first and now classical example of modular structures established by Thompson (1978). He showed that the structures of micas, pyroxenes and amphiboles share, according to different ratios, the same modules of mica ( M ) and pyroxene ( P ) and are members of a polysomatic series MmPp . The ideal chemical composition and cell parameters of the members of the series are linear functions of the ratio m / p . The classification of biopyriboles as members of a polysomatic series, a type of series belonging to the wider category of the homologous series (cf. Ferraris et al. 2004), and the consequent discovery of the multiple-chain-width biopyriboles jimthompsonite and chesterite (Veblen and Buseck 1979) dramatically proved the predictive power of these series in terms of structure characterization and modeling. The modeling of carlosturanite (Mellini et al. 1985) and of other modular structures …

Kristiansenite occurs as a late hydrothermal mineral in vugs in an amazonite pegmatite at Heftetjern, Tordal, Telemark, Norway. Tapering crystals, rarely up to 2 mm long, are colourless, white, or slightly yellowish. The mineral has the ideal composition Ca2ScSn(Si2O7)(Si2O6OH) and is triclinic C1 with cell parameters a = 10.028(1), b = 8.408(1), c = 13.339(2) A, α = 90.01(1), β = 109.10(1), γ = 90.00(1)°, V = 1062.7(3) A3 (Z = 4). It has a monoclinic cell within ∼ 0.1 A and is polysynthetically twinned on {010} by metric merohedry. The strongest reflections in the X-ray powder pattern are [d in A, (I obs), (hkl)]: 5.18 (53) (1–11), 3.146 (100) (004), 3.089 (63) (−222), 2.901 (19) (221), 2.595 (34) (222), 2.142 (17) (−3–31). The Mohs’ hardness is 5½–6; Dcalc. = 3.64 g/cm3; only a mean refractive index of 1.74 could be measured. Scandium enrichment in the Heftetjern pegmatite and the crystal chemistry of scandium are briefly discussed.

The structure refinement of associated phlogopite-2 O and phlogopite-1 M from the Khibiny massif (Kola Peninsula, Russia) is reported. Crystal data are: α = 5.2781(5), b = 9.141(1), c = 20.124(4) A, Ccmm (20); a = 5.305(2), b = 9.199(2), c = 10.232(4) A, β = 100.03(2)°, C 2/m (1 M ). Least-squares refinement of single-crystal X-ray diffraction data converged to R1 = 0.034 (2 O , 926 independent reflections) and 0.037 (1 M , 677 independent reflections). This is the first structure refinement of an MDO (standard) mica-2 O : two previous structure reports concerned anandite-2 O , which was not a true polytype, having an oP (primitive orthorhombic) lattice not compatible with the C -centred cell common to all mica polytypes. The two phlogopite polytypes show practically the same chemical composition (K 0 . 95Na 0.01 ) (Mg 2.16 Fe 0.34 Ti 0.04 Mn 0.04 Li 0.40 )[Si 3.40 Al 0.60 O 10 ][(OH) 1.35 F 0 .65] and no cation ordering. Both polytypes are affected by stacking disorder, which broadens the non-family reflections ( k ≠ 3n). As a consequence, the diffracted intensities of the two types are measured at different scales and large residues in the difference Fourier maps were observed at ± b /3 along [010], [310] and [310]. These residues ( uroviceffect ) disappear by carrying out the refinement with separate scale factors for the two types of reflections. On the basis of structural, morphology and zoning considerations the formation of the two associated polytypes is attributed to chemical oscillation in the crystallization mean.

The structure of the new disilicate kristiansenite, Ca2ScSn(Si2O7)(Si2O6OH), has been solved and refined from a crystal polysynthetically twinned by metric merohedry. The Bravais lattice is mC, with parameters a = 10.028(1), b = 8.408(1), c = 13.339(2) Å, α = 90.01(1), β = 109.10(1), γ = 90.00(1)°, but the space-group type is C1 (Z = 4). The twin law is m´, and the two components of the twin have nearly identical volumes: as a consequence, the Laue group of the twin is practically 2/m. By taking into account the twinning, an anisotropic refinement of the structure in C1 converged to R1 = 0.0242 for 259 refined parameters and 4862 observed reflections. The effects of the twinning by metric merohedry and of the volume ratio of the components on the symmetry of the diffraction pattern are discussed. The triclinic structure approximates within about 0.1 Å the monoclinic symmetry, the lower symmetry resulting mainly from cation ordering. Kristiansenite represents a new type of silicate structure and the first known case with the presence of protonated and normal disilicate groups at the same time. The disilicate groups and the other polyhedra centred on cations lie on different alternating (101) planes.