R. K. Rastsvetaeva

Structural mineralogy of the eudialyte group: A review

New data on the chemical composition and structure of minerals of the eudialyte group are reviewed with respect to their classification; structural prerequisites of their properties; and structural changes occurring upon isomorphous substitutions, decationization, hydration, and solid-phase transformations of eudialyte due to the processes of potassium metasomatism. The problems associated with the separation of mineral species are considered within the structural-chemical approach. The nomenclature of mineral species, their typomorphism, and a number of other problems important for modern mineralogy are discussed.

Crystal structure of deloryite, Cu4(UO2)[Mo2O8](OH)6

Deloryite, Cu4(UO2)[Mo2O8](OH)6, M = 946.10, monoclinic, space group C2/m, a = 19.94(1), b = 6.116(2), c = 5.520(3) A, β = 104.18(5)°, V = 652.8(1) A3, Z = 2, ρc = 4.78 g cm−3, λ(Mo Kα) = 0.71073 A, μ = 200.22 cm−1, dimensions 0.15 × 0.1 × 0.1 mm3, F(000) = 852, room temperature, R = 0.064 for 402 reflections with |bF| > 3σ(F). The crystal structure of deloryite, like its synthetic analogue as well as chemically and crystallographically related derriksite Cu4(UO2)(SeO3)2(OH)6, contains layers formed by distorted [Cu(O,OH)6] octahedra with shared edges. The octahedral layers are linked by columns, built up of alternating pseudotetragonal U[2+4]O6 bipyramids and pseudotrigonal Mo[4+1]O5 bipyramids. Two MoO5 bipyramids with shared edge form [Mo2O8] dimers with Mo-Mo distances = 3.456(4) A. The five-fold coordination of Mo revealed leads to a different description of the structural model of deloryite with respect to the earlier XRD study of its synthetic analogue. Mo2[4+1]O8 dimers in deloryite replace the pairs of tetrahedra SeO3E (E = lone-pair electrons) in derriksite.

Surkhobite: revalidation and redefinition with the new formula, (Ba, K)2CaNa(Mn, Fe2+, Fe3+)8Ti4(Si2O7)4O4(F, OH, O)6

Surkhobite, a new mineral related to the members of the jinshajiangite-perraultite series, was approved in 2002 (IMA No. 2002-037) and later discredited (IMA decision 06-E). It is redefined here with a new formula and revalidated with the original name (IMA 07-A). It occurs as platy crystals up to 1 mm and grains up to 2 × 1 × 0.4 cm in the association with aegirine, microcline, albite, quartz, amphibole, annite, bafertisite, astrophyllite, zircon, fluorite, polylithionite, stillwelite, sogdianite, tadjikite in alkaline pegmatite at the massif Dara-i-Pioz, Tajikistan. Surkhobite is translucent, brownish-red, lustre vitreous, streak white, cleavage perfect on {001}; hardness is anisotropic: the minimum value H 1 = 250 kg/mm 2 , the maximum value H 2 = 482 kg/mm 2 ; Mohs’ hardness is 4½. Biaxial, negative, β= 1.858(10), γ= 1.888(10); 2 V = 65(5)°; α= 1.790 (calculated from 2 V ). Optical orientation: X = b , Z ∧ a = 34°. Dispersion is strong, r . Pleochroism: Y (orange) > Z (bright-yellow) ≥ X (yellow). Microtwinning on (001) is observed. D calc = 3.98 g/cm 3 ; D meas = 3.84(10) g/cm 3 . IR and Mossbauer spectra are given. Chemical composition is (electron microprobe combined with Mossbauer data, wt.%): Na 2 O 2.27, K 2 O 1.87, CaO 2.53, SrO 0.26, BaO 11.16, MgO 0.13, MnO 16.32, FeO 13.92, Fe 2 O 3 2.11, Al 2 O 3 0.02, SiO 2 27.17, TiO 2 16.14, Nb 2 O 5 2.14, ZrO 2 0.34, F 2.94, H 2 O (by Penfield method) 1.17, -O=F 2 –1.24, total 99.25. The empirical formula is ( Z = 2): Na 2.60 K 1.41 Ca 1.60 Sr 0.09 Ba 2.58 (Mn 8.17 Fe 2+ 6.88 Fe 3+ 0.94 Mg0. 115 Al 0.01 ) ∑16.115 (Ti 7.17 Nb 0.57 Zr 0.10 ) ∑7.84 Si 16.06 H 4.61 F 5.49 O 70.51 . The simplified formula, taking into account the crystal structure, is ( Z = 2): KBa 3 Ca 2 Na 2 (Mn, Fe 2+ , Fe 3+ ) 16 Ti 8 (Si 2 O 7 ) 8 O 8 (OH) 4 (F,O,OH) 8 . The crystal structure was refined on a single crystal to R = 0.043 with 3686 independent reflections ( F > 2σ). Surkhobite is monoclinic, C 2, a = 10.723(1), b = 13.826(2), c = 20.791(4) A, β = 95.00(1)°. Surkhobite is the Mn-dominant analogue of jinshajiangite and differs from perraultite in that Ca is ordered onto and is dominant in the site A (6). The strongest lines of the powder difraction pattern [ d , A ( I , %) ( hkl )] are: 10.39 (20) (002), 3.454 (100) (006), 3.186 (15) (321), 2.862 (15) (225), 2.592 (70) (008), 2.074 (40) (048).

Crystal structure of new micalike titanosilicate—bussenite, Na2Ba2Fe2+[TiSi2O7][CO3]O(OH)(H2O)F

AbstractThe crystal structure of mineral bussenite, Na2Ba2Fe[TiSi2O7][CO3]O(OH)(H2O)F, found in the Khibiny massif (the Kola Peninsula) has been determined. The parameters of the triclinic unit-cell are a = 5.399(3) Å, b = 7.016(9) Å, c = 16.254(14) Å, α = 102.44(8)°, β = 93.18(6)°, γ = 90.10(7)°, sp. gr.

Crystal structure of surkhobite: New mineral from the family of titanosilicate micas

P\bar 1

The crystal structure of emmerichite Ва 2Na 3Fe 3+Ti 2(Si 2O 7) 2O 2F 2, a new lamprophyllite-group mineral

, R = 0.054 for 1418 reflections with |F| > 2.5σ(F). The mineral studied belongs to the family of layered titanosilicates, in which, unlike the sulfate-and phosphate-containing representatives of this family, the interlayer spaces are filled with carbonate groups.

Footemineite, the Mn-analog of atencioite, from the Foote mine, Kings Mountain, Cleveland County, North Carolina, U.S.A., and its relationship with other roscherite-group minerals

The new Mg- and F-dominant lamprophyllite-group mineral lileyite (IMA 2011-021) was found at the Lohley quarry, Udersdorf, near Daun, Eifel Mountains, Rhineland-Palatinate (Rheinland-Pfalz), Germany, and named for the old name of the type locality, Liley. Associated minerals are nepheline, leucite, augite, magnetite, fluorapatite, perovskite, gotzenite. Lileyite is brown, translucent; streak is white. It forms platy crystals up to 0.1 × 0.3 × 0.5 mm in size and their clusters up to 1 mm across on the walls of cavities in an alkaline basalt. Lileyite is brittle, with Mohs hardness of 3–4 and perfect cleavage on (001). D calc is 3.776 g/cm 3 . The new mineral is biaxial (+), α = 1.718(5), β = 1.735(5), γ = 1.755(5), 2V (meas.) = 75(15)°, 2V (calc.) = 86°. The IR spectrum is given. The chemical composition is (EDS-mode electron microprobe, mean of 5 analyses, wt%): SiO 2 28.05, BaO 26.39, TiO 2 18.53, Na 2 O 6.75, MgO 4.58, FeO 4.48, CaO 2.30, SrO 2.23, MnO 1.44, K 2 O 1.41, Nb 2 O 5 0.95, F 3.88, –O=F 2 -1.63; total 99.36. The empirical formula based on 18 anions is: Ba 1.50 Sr 0.19 K 0.26 Na 1.89 Ca 0.36 Mn 0.18 Mg 0.99 Fe 0.54 Ti 2.01 Nb 0.06 Si 4.06 O 16.23 F 1.77 . The simplified formula is: Ba 2 (Na,Fe,Ca) 3 MgTi 2 (Si 2 O 7 ) 2 O 2 F 2 . The crystal structure was solved using single-crystal X-ray diffraction data ( R = 0.024). Lileyite is monoclinic, space group C 2/ m , a = 19.905(1), b = 7.098(1), c = 5.405(1) A, β = 96.349(5)°, V = 758.93(6) A 3 , Z = 2. The strongest lines of the powder diffraction pattern [ d , A ( I , %) ( hkl )] are: 3.749 (45) (31–1), 3.464 (76) (510, 311, 401), 3.045 (37) (51–1), 2.792 (100) (221, 511), 2.672 (54) (002, 601, 20-2), 2.624 (43) (710, 42–1). Type material is deposited in the collections of the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia, registration number 4106/1.

Kyanoxalite, a new cancrinite-group mineral species with extraframework oxalate anion from the Lovozero alkaline pluton, Kola peninsula

The crystal structure of surkhobite, a new mineral from Tajikistan, was determined by methods of X-ray diffraction analysis (a = 10.723 Å, b = 13.826 Å, c = 20.791 Å, β = 95°, sp. gr. C2, R = 0.047). The structure is a derivative of the bafertisite structure but differs from it and other representatives of the titanosilicate micas: three-layered slabs are connected to form isolated channels orderly filled with Ca, Na, Ba, and K atoms.