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  • 1
    Publication Date: 2015-12-16
    Description: The crystal structure of betalomonosovite, ideally Na 6 4 Ti 4 (Si 2 O 7 ) 2 [PO 3 (OH)][PO 2 (OH) 2 ]O 2 (OF), a 5.3331(7), b 14.172(2), c 14.509(2) Å, α 103.174(2), β 96.320(2), 90.278(2)°, V 1060.7(4) Å 3 , from the Lovozero alkaline massif, Kola peninsula, Russia, has been refined in the space group P 1{macron} to R = 6.64% using 3379 observed ( F o 〉 4 F ) reflections collected with a single-crystal APEX II ULTRA three-circle diffractometer with a rotating-anode generator (Mo K α), multilayer optics, and an APEX-II 4K CCD detector. Electron-microprobe analysis gave the empirical formula (Na 5.39 Ca 0.36 Mn 0.04 Mg 0.01 ) 5.80 (Ti 2.77 Nb 0.48 Mg 0.29 Fe 3+ 0.23 Mn 0.20 Zr 0.02 Ta 0.01 ) 4 (Si 2.06 O 7 ) 2 [P 1.98 O 5 (OH) 3 ]O 2 [O 0.82 F 0.65 (OH) 0.53 ] 2 , D calc. = 2.969 g cm –3 , Z = 2, calculated on the basis of 26 (O + F) apfu , with H 2 O determined from structure refinement. The crystal structure of betalomonosovite is characterized by extensive cation and anion disorder: more than 50% of cation sites are partly occupied. The crystal structure of betalomonosovite is a combination of a titanium silicate (TS) block and an intermediate ( I ) block. The TS block consists of HOH sheets (H-heteropolyhedral, O-octahedral) and exhibits linkage and stereochemistry typical for Group IV (Ti + Mg + Mn = 4 apfu ) of the TS-block minerals. The I block is a framework of Na polyhedra and P tetrahedra which ideally gives {Na 2 4 [PO 3 (OH)][PO 2 (OH) 2 ]} pfu . Betalomonosovite is an Na-poor OH-bearing analogue of lomonosovite, Na 10 Ti 4 (Si 2 O 7 ) 2 (PO 4 ) 2 O 4 . In the betalomonosovite structure, there is less Na in the I block and in the TS block when compared to the lomonosovite structure. The OH groups occur mainly in the I block where they coordinate P and Na atoms and in the O sheet of the TS block (minor). The presence of OH groups in the I block and in the TS block is supported by IR spectroscopy and bond-valence calculations on anions. High-resolution TEM of lomonosovite shows the presence of pervasive microstructural intergrowths, accounting for the presence of signals from H 2 O in the infrared spectrum of anhydrous lomonosovite. More extensive lamellae in betalomonosovite suggest a topotactic reaction from lomonosovite to betalomonosovite.
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  • 2
    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉The crystal structure of polylithionite-1〈span〉M〈/span〉 from Darai-Pioz, (K〈sub〉0.97〈/sub〉Na〈sub〉0.03〈/sub〉Rb〈sub〉0.01〈/sub〉)〈sub〉Σ1.01〈/sub〉(Li〈sub〉2.04〈/sub〉Al〈sub〉0.84〈/sub〉 Ti〈sup〉4+〈/sup〉〈sub〉0.09〈/sub〉Fe〈sup〉3+〈/sup〉〈sub〉0.03〈/sub〉)〈sub〉Σ3.00〈/sub〉(Si〈sub〉3.98〈/sub〉Al〈sub〉0.02〈/sub〉)O〈sub〉10〈/sub〉[F〈sub〉1.68〈/sub〉(OH)〈sub〉0.33〈/sub〉]〈sub〉Σ2〈/sub〉, 〈span〉a〈/span〉 5.1974(4), 〈span〉b〈/span〉 8.9753(6), 〈span〉c〈/span〉 10.0556(7) Å, β 100.454(1)°, 〈span〉V〈/span〉 461.30(6) Å〈sup〉3〈/sup〉, space group 〈span〉C〈/span〉2, 〈span〉Z〈/span〉 = 2, was refined to 〈span〉R〈/span〉〈sub〉1〈/sub〉 = 1.99% using Mo〈span〉K〈/span〉α X-radiation. In the space group 〈span〉C〈/span〉2, there are three octahedrally coordinated 〈span〉M〈/span〉 sites in the 1〈span〉M〈/span〉 mica structure: the 〈span〉M〈/span〉(1) site is occupied by Li〈sup〉+〈/sup〉 and minor vacancy that is likely locally associated with Ti〈sup〉4+〈/sup〉 at the 〈span〉M〈/span〉(2) site; the 〈span〉M〈/span〉(2) site is occupied dominantly by Al〈sup〉3+〈/sup〉, with other minor divalent to tetravalent cations; the 〈span〉M〈/span〉(3) site is completely occupied by Li〈sup〉+〈/sup〉. In the space group 〈span〉C〈/span〉2, the structure is completely ordered. Each non-bridging O〈sup〉2–〈/sup〉 ion is surrounded by an ordered arrangement of 2Li〈sup〉+〈/sup〉 + Al〈sup〉3+〈/sup〉 + Si〈sup〉4+〈/sup〉 with an incident bond-valence sum of 1.95 〈span〉vu〈/span〉 (valence units). The F〈sup〉–〈/sup〉 ion is coordinated by Li〈sup〉+〈/sup〉 + Li〈sup〉+〈/sup〉 + Al〈sup〉3+〈/sup〉 with an incident bond-valence sum of 0.84 〈span〉vu〈/span〉 (values around F〈sup〉–〈/sup〉 generally tend to be lower than ideal). Thus, the valence-sum rule is satisfied, both long range and short range. In the space group 〈span〉C〈/span〉2/〈span〉m〈/span〉, there is long-range order but not short-range order. There are three different short-range arrangements, one of which has bond-valence deficiencies of 0.38 and 0.49 〈span〉vu〈/span〉 around the non-bridging O〈sup〉2–〈/sup〉 ion and the F〈sup〉–〈/sup〉 ion, destabilizing the structure relative to the more ordered arrangement of the 〈span〉C〈/span〉2 structure, which conforms more closely to the valence-sum rule. The drive to lower the symmetry in polylithionite-1〈span〉M〈/span〉 from 〈span〉C〈/span〉2/〈span〉m〈/span〉 to 〈span〉C〈/span〉2 comes from the short-range bond-valence requirements of the structure.〈/span〉
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  • 3
    Publication Date: 2014-02-12
    Description: The crystal structure of schüllerite, ideally Na 2 Ba 2 Mg 2 Ti 2 (Si 2 O 7 ) 2 O 2 F 2 , a 5.396(1), b 7.071(1), c 10.226(2) Å, α 99.73(3), β 99.55(3), 90.09(3)°, V 379.1(2) Å 3 , Z = 1, from the Eifel volcanic region, Germany, has been refined in the space group P 1 to R = 1.33% using 2247 observed ( F o 〉 4 F ) reflections collected with a single-crystal Bruker D8 three-circle diffractometer equipped with a rotating-anode generator (Mo K α radiation), multilayer optics and an APEX-II detector. The empirical formula for schüllerite was calculated on the basis of 18 (O + F) anions: (Na 1.10 Ca 0.43 Mn 0.30 Fe 2+ 0.17 ) 2 (Ba 1.57 Sr 0.14 K 0.14 0.15 ) 2 (Mg 0.79 Fe 2+ 0.71 Na 0.33 Fe 3+ 0.17 ) 2 (Ti 1.67 Fe 3+ 0.21 Nb 0.09 Zr 0.02 Al 0.01 ) 2 Si 3.95 O 15.93 F 2.07 , D calc. = 3.879 g/cm 3 , Z = 1, with Fe 3+ / (Fe 2+ +Fe 3+ ) ratio determined by Mössbauer spectroscopy. Schüllerite is a Group-IV TS-block mineral: Ti + Mg = 4 apfu . The crystal structure of schüllerite is an alternation of TS (Titanium Silicate) and I (intermediate) blocks of the ideal composition [Na 2 Mg 2 Ti 2 (Si 2 O 7 ) 2 O 2 F 2 ] 4– and [Ba 2 ] 4+ , respectively. The TS block is composed of the central O (octahedral) sheet and two adjacent H (heteropolyhedral) sheets. In the O sheet, there are two brookite-like chains of M O octahedra of the following ideal compositions: [Mg 2 O 8 ] 12– [M O (1)] and [Na 2 O 8 ] 14– [M O (2)]; the ideal composition of the O sheet is [Na 2 Mg 2 O 2 F 2 ] 0. The H sheet is composed of the [5]-coordinated Ti-dominant M H polyhedra and Si 2 O 7 groups; the composition of the two H sheets is [Ti 2 (Si 2 O 7 ) 2 ] 4–. In schüllerite, the TS block has a topology characteristic of Group IV of TS-block minerals: two H sheets connect to the O sheet such that two Si 2 O 7 groups link to the Mg-dominant octahedra of the O sheet adjacent along t 1 . In the O sheet, occurrence of divalent cations at the M O (1) site results in the presence of monovalent anions, F – , at the X O A site. The A P site of the H sheet is occupied mainly by Ba; the A P site is shifted from the plane of the H sheet, and Ba atoms constitute the I block of the composition [Ba 2 ] 4+ . Schüllerite is the only mineral of Group IV that has (1) a brookite-like [Mg 2 O 8 ] 12– chain of octahedra in the O sheet; (2) [5]-coordinated Ti in the H sheet; (3) Ba atoms in the I block. The ideal structural formula of schüllerite is of the form A P 2 M H 2 M O 4 (Si 2 O 7 ) 2 (X O M ) 2 (X O A ) 2 : Ba 2 Ti 2 Na 2 Mg 2 Ti 2 (Si 2 O 7 ) 2 O 2 F 2 , Z = 1.
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  • 4
    Publication Date: 2014-10-22
    Description: The HOH layer is the main structural unit in the crystal structures of Fe 3+ -disilicates ericssonite-2 O , ideally Ba 2 Fe 3+ 2 Mn 4 (Si 2 O 7 ) 2 O 2 (OH) 2 , ferroericssonite, ideally Ba 2 Fe 3+ 2 Fe 2+ 4 (Si 2 O 7 ) 2 O 2 (OH) 2 , and yoshimuraite, ideally Ba 4 Ti 2 Mn 4 (Si 2 O 7 ) 2 (PO 4 ) 2 O 2 (OH) 2 , a TS-block mineral of Group II. The chemical compositions of the core part of the HOH layer in ericssonite-2 O and ferroericssonite, [5] Fe 3+ 2 Mn 4 (Si 2 O 7 ) 2 O 2 (OH) 2 and [5] Fe 3+ 2 Fe 2+ 4 (Si 2 O 7 ) 2 O 2 (OH) 2 , are similar to the chemical composition of the core part of the HOH layer in yoshimuraite, [5] Ti 4+ 2 Mn 4 (Si 2 O 7 ) 2 O 2 (OH) 2 , except for the cation species at the [5]-coordinated M H site in the H sheets: [5] Fe 3+ and [5] Ti 4+ , respectively. Despite this similarity, the topology of the HOH layer in ericssonite-2 O and ferroericssonite is different from that in yoshimuraite. In TS-block minerals, different distortions of M O octahedra correspond to specific types of linkage of H and O sheets. Topological consideration of Fe 3+ -disilicates ericssonite-2 O and ferroericssonite and yoshimuraite, a TS-block mineral of Group II, shows that different topologies of the chemically identical HOH layer are due to a difference in the bond-valence contributions of Fe 3+ and Ti 4+ at the M H site in the H sheet ( i.e. , inability of Fe 3+ to contribute sufficient bond-valence to the X O M anion) and subsequent different distortions of M O octahedra in the O sheet, where M O = Mn 2+ , Fe 2+ .
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  • 5
    Publication Date: 2015-03-26
    Description: A bstract Saamite, BaTiNbNa 3 Ti(Si 2 O 7 ) 2 O 2 (OH) 2 (H 2 O) 2 , is a Group-III TS-block mineral from the Kirovskii mine, Mount Kukisvumchorr, Khibiny alkaline massif, Kola Peninsula, Russia. The mineral occurs as transparent platy crystals 2–10 μm thick and up to 180 μm across. It is colorless to very pale tan, with a white streak and a vitreous luster. The mineral formed in a pegmatite as a result of hydrothermal activity. Associated minerals are natrolite, barytolamprophyllite, kazanskyite, nechelyustovite, hydroxylapatite, belovite-(La), belovite-(Ce), gaidonnayite, nenadkevichite, epididymite, apophyllite-(KF), and sphalerite. Saamite has perfect cleavage on {001}, uneven fracture and a Mohs hardness ca. 3. Its calculated density is 3.243 g/cm 3 . Saamite is biaxial positive with α 1.760, β 1.770, 1.795 ( 589 nm), 2 V meas. = 69(2)°, 2 V calc. = 65°, with medium dispersion, r 〉 v . It is nonpleochroic. Saamite is triclinic, space group P 1 {macron} , a 5.437(2), b 7.141(3), c 21.69(1) Å, α 92.97(1), β 96.07(1), 90.01(1)°, V 836.3(11) Å 3 . The strongest lines in the X-ray powder-diffraction pattern [ d (Å)(I)( hkl )] are: 21.539(100)(001), 2.790(15)(122), 2.692(14)(008), 3.077(13)(007), 7.180(11)(003), 2.865(11)(1 2 {macron} 2), 1.785(9)(1 1 {macron} 4), 2.887(9)( 1 {macron} 22, 0 1 {macron} 7, 115), and 1.785(9)(0 4 {macron} 1, 1 3 {macron} 7, 040, 2 {macron} 2 {macron} 8, 230, 23 1 {macron} ). Chemical analysis by electron microprobe gave Nb 2 O 5 12.24, TiO 2 20.37, SiO 2 29.07, Al 2 O 3 0.08, FeO 0.32, MnO 5.87, MgO 0.04, BaO 11.31, SrO 2.51, CaO 1.76, K 2 O 0.77, Na 2 O 8.39, H 2 O 5.77, F 1.71, O = F –0.72, sum 99.49 wt.%; H 2 O was determined from structure refinement and its presence was confirmed by IR spectroscopy. The empirical formula based on 20 (O + F) atoms pfu is (Ba 0.61 Sr 0.20 K 0.13 0.06 ) 1 ( 0.74 Ca 0.26 ) 1 ( Na 2.22 Mn 0.55 Fe 0.04 2 + 0.19 ) 3 (Ti 2.09 Nb 0.76 Mn 0.13 Mg 0.01 Al 0.01 ) 3 Si 3.97 O 19.26 H 5.26 F 0.74 , Z = 2. The simplified formula is as follows: Ba(,Ca)Ti(Nb,Ti)(Na,Mn) 3 (Ti,Nb)(Si 2 O 7 ) 2 O 2 (OH,F) 2 (H 2 O) 2 . The IR spectrum of saamite contains the following bands: ~1605, 1645, ~1747 and ~3420 cm –1 . The crystal structure was solved by direct methods and refined to an R 1 index of 9.92%. In the crystal structure of saamite, the main structural unit is the TS block, which consists of HOH sheets (H-heteropolyhedral, O-octahedral). The TS block exhibits linkage and stereochemistry typical for Group III [Ti (+ Nb + Mg) = 3 apfu ] of TS-block minerals. The O sheet is composed of Na- and Ti-dominant octahedra and has ideal composition Na 3 Ti apfu . The TS block has two different H sheets where Si 2 O 7 groups link to [5]-coordinated Ti and [6]-coordinated Nb polyhedra, respectively. There are two peripheral sites, [10]-coordinated A P (1) and [8]-coordinated A P (2), occupied mainly by Ba (less Sr and K) at 94% and Ca at 26%, respectively. In the crystal structure of saamite, adjacent TS blocks connect in two different ways: (1) via hydrogen bonds between H 2 O–H 2 O groups and H 2 O–O atoms of adjacent TS blocks; (2) via a layer of Ba atoms that constitute the I block. The TS block, I block and types of self-linkage of TS blocks are topologically identical to those in the nechelyustovite structure. The mineral is named after the Saami (Caam in Cyrillic) indigenous people who inhabit parts of the Kola Peninsula of Russia, far northern Norway, Sweden, and Finland.
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  • 6
    Publication Date: 2014-03-25
    Description: Kolskyite, (Ca)Na 2 Ti 4 (Si 2 O 7 ) 2 O 4 (H 2 O) 7 , is a Group-IV TS-block mineral from the Kirovskii mine, Mount Kukisvumchorr, Khibiny alkaline massif, Kola Peninsula, Russia. The mineral occurs as single, platy crystals 2–40 μm thick and up to 500 μm across. It is pinkish yellow, with a white streak and a vitreous luster. The mineral formed in a pegmatite as a result of hydrothermal activity. Associated minerals are natrolite, nechelyustovite, kazanskyite, barytolamprophyllite, hydroxylapatite, belovite-(La), belovite-(Ce), gaidonnayite, nenadkevichite, epididymite, apophyllite-(KF), and sphalerite. Kolskyite has perfect cleavage on {001}, splintery fracture, and a Mohs hardness of 3. Its calculated density is 2.509 g/cm 3 . Kolskyite is biaxial negative with α 1.669, β 1.701, 1.720 ( 590 nm), 2 V meas. = 73.6(5)°, 2 V calc. = 74.0°, with no discernible dispersion. It is nonpleochroic. Kolskyite is triclinic, space group P , a 5.387(1), b 7.091(1), c 15.473(3) Å, α 96.580(4), β 93.948(4), 89.818(3)°, V 585.8(3) Å 3 . The strongest lines in the X-ray powder-diffraction pattern [ d (Å)(I)( hkl )] are: 15.161(100)(001), 2.810(19)(121, 12), 3.069(12) (005), 2.938(10)(1,120,11), 2.680(9)(3, 200,114, 01), 1.771(9) (04,040), 2.618(8)(13,122), 2.062(7)(221,22,3,22), and 1.600(7)(2,320,320). Chemical analysis by electron microprobe gave Nb 2 O 5 6.96, ZrO 2 0.12, TiO 2 26.38, SiO 2 27.08, FeO 0.83, MnO 2.95, MgO 0.76, BaO 3.20, SrO 5.21, CaO 4.41, K 2 O 0.79, Na 2 O 6.75, H 2 O 13.81, F 0.70, O = F –0.29, sum 99.66 wt.%; H 2 O was determined from structure solution and refinement. The empirical formula was calculated on 25 (O + F) apfu : (Na 1.93 Mn 0.04 Ca 0.03 ) 2 (Ca 0.67 Sr 0.45 Ba 0.19 K 0.15 ) 1.46 (Ti 2.93 Nb 0.46 Mn 0.33 Mg 0.17 Fe 2+ 0.10 Zr 0.01 ) 4 Si 4.00 O 24.67 H 13.60 F 0.33 , Z = 1. Simplified and ideal formulae are as follows: (Ca,) 2 Na 2 Ti 4 (Si 2 O 7 ) 2 O 4 (H 2 O) 7 and (Ca)Na 2 Ti 4 (Si 2 O 7 ) 2 O 4 (H 2 O) 7 . The FTIR spectrum of the mineral contains the following bands: ~3300 cm –1 (very broad) and ~1600 cm –1 (sharp). The crystal structure was solved by direct methods and refined to an R 1 index of 8.8%. The crystal structure of kolskyite is a combination of a TS (titanium-silicate) block and an I (intermediate) block. The TS block consists of HOH sheets (H-heteropolyhedral, O-octahedral). The TS block exhibits linkage and stereochemistry typical for Group IV [Ti (+ Mg + Mn) = 4 apfu ] of Ti-disilicate minerals. In the H sheet in kolskyite, Si 2 O 7 groups link to [6]-coordinated Ti octahedra. In the O sheet, Ti-dominant and Na octahedra each form brookite-like chains. There is one peripheral A P site occupied mainly by Ca (less Sr, Ba, and K) at 68%. The I block consists of H 2 O groups and A P atoms. The I block is topologically identical to those in the kazanskyite and nechelyustovite structures. The mineral is named after the Kola Peninsula ( Kolskyi Poluostrov in Russian). The chemical formula and structure of kolskyite were predicted by Sokolova & Cámara (2010) ; this is the first correct prediction of a TS-block mineral.
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  • 7
    Publication Date: 2014-03-25
    Description: New developments in crystal chemistry have been considered for 34 titanium disilicate minerals that contain the TS (Titanium-Silicate) block, a central trioctahedral (O) sheet, and two adjacent heteropolyhedral (H) sheets of [5–7]-coordinated polyhedra and Si 2 O 7 groups. The general formula of the TS block is A P 2 B P 2 M H 2 M O 4 (Si 2 O 7 ) 2 X 4+n , where M H 2 and M O 4 = cations of the H and O sheets; M H = Ti, Nb, Zr, Mn, Ca + REE, Ca; M O = Ti, Zr, Nb, Fe 2+ , Mg, Mn, Ca, Na; A P and B P = cations at the peripheral ( P ) sites = Na, Ca + REE, Ca, Ba, Sr, K; X = anions, O, OH, F, and H 2 O groups; X 4+n = X O 4 + X P n , n = 0, 1, 1.5, 2, 4. There are three topologically distinct TS blocks based on three types of linkage of H and O sheets. In the crystal structures of TS-block minerals, TS blocks either link directly or alternate with intermediate ( I ) blocks. The I block consists of alkali and alkaline-earth cations, oxyanions (PO 4 ), (SO 4 ) and (CO 3 ), and H 2 O groups. There are four groups of TS-block structures, based on the topology and stereochemistry of the TS block: Groups I, II, III, and IV, where Ti (+ Nb + Zr + Mg + Mn) = 1, 2, 3, and 4 apfu , respectively. In a TS-block structure, four types of self-linkage between adjacent TS blocks occur. The concept of basic and derivative structures has been introduced for TS-block minerals. A basic structure has the following four characteristics: (1) there is only one type of TS block; (2) the two H sheets of the TS block are identical; (3) there is only one type of I block, or it is absent; and (4) there is only one type of self-linkage of TS blocks. Basic structures obey the general structural principles of Sokolova (2006) . A derivative structure has one or more of the three following characteristics: (1) there is more than one type of TS block; (2) there is more than one type of I block; (3) there is more than one type of self-linkage of TS blocks. A derivative structure is related to two or more basic structures of the same Group: it can be derived by adding these structures via sharing the central O sheet of the TS blocks of adjacent structural fragments which represent basic structures . There are 30 basic TS-block structures and four derivative TS-block structures. Based on established relations between basic and derivative structures, possible atomic arrangements and chemical formulae have been predicted for 12 derivative structures and two basic structures.
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  • 8
    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉The crystal structure of polylithionite-1〈span〉M〈/span〉 from Darai-Pioz, (K〈sub〉0.97〈/sub〉Na〈sub〉0.03〈/sub〉Rb〈sub〉0.01〈/sub〉)〈sub〉Σ1.01〈/sub〉(Li〈sub〉2.04〈/sub〉Al〈sub〉0.84〈/sub〉 Ti〈sup〉4+〈/sup〉〈sub〉0.09〈/sub〉Fe〈sup〉3+〈/sup〉〈sub〉0.03〈/sub〉)〈sub〉Σ3.00〈/sub〉(Si〈sub〉3.98〈/sub〉Al〈sub〉0.02〈/sub〉)O〈sub〉10〈/sub〉[F〈sub〉1.68〈/sub〉(OH)〈sub〉0.33〈/sub〉]〈sub〉Σ2〈/sub〉, 〈span〉a〈/span〉 5.1974(4), 〈span〉b〈/span〉 8.9753(6), 〈span〉c〈/span〉 10.0556(7) Å, β 100.454(1)°, 〈span〉V〈/span〉 461.30(6) Å〈sup〉3〈/sup〉, space group 〈span〉C〈/span〉2, 〈span〉Z〈/span〉 = 2, was refined to 〈span〉R〈/span〉〈sub〉1〈/sub〉 = 1.99% using Mo〈span〉K〈/span〉α X-radiation. In the space group 〈span〉C〈/span〉2, there are three octahedrally coordinated 〈span〉M〈/span〉 sites in the 1〈span〉M〈/span〉 mica structure: the 〈span〉M〈/span〉(1) site is occupied by Li〈sup〉+〈/sup〉 and minor vacancy that is likely locally associated with Ti〈sup〉4+〈/sup〉 at the 〈span〉M〈/span〉(2) site; the 〈span〉M〈/span〉(2) site is occupied dominantly by Al〈sup〉3+〈/sup〉, with other minor divalent to tetravalent cations; the 〈span〉M〈/span〉(3) site is completely occupied by Li〈sup〉+〈/sup〉. In the space group 〈span〉C〈/span〉2, the structure is completely ordered. Each non-bridging O〈sup〉2–〈/sup〉 ion is surrounded by an ordered arrangement of 2Li〈sup〉+〈/sup〉 + Al〈sup〉3+〈/sup〉 + Si〈sup〉4+〈/sup〉 with an incident bond-valence sum of 1.95 〈span〉vu〈/span〉 (valence units). The F〈sup〉–〈/sup〉 ion is coordinated by Li〈sup〉+〈/sup〉 + Li〈sup〉+〈/sup〉 + Al〈sup〉3+〈/sup〉 with an incident bond-valence sum of 0.84 〈span〉vu〈/span〉 (values around F〈sup〉–〈/sup〉 generally tend to be lower than ideal). Thus, the valence-sum rule is satisfied, both long range and short range. In the space group 〈span〉C〈/span〉2/〈span〉m〈/span〉, there is long-range order but not short-range order. There are three different short-range arrangements, one of which has bond-valence deficiencies of 0.38 and 0.49 〈span〉vu〈/span〉 around the non-bridging O〈sup〉2–〈/sup〉 ion and the F〈sup〉–〈/sup〉 ion, destabilizing the structure relative to the more ordered arrangement of the 〈span〉C〈/span〉2 structure, which conforms more closely to the valence-sum rule. The drive to lower the symmetry in polylithionite-1〈span〉M〈/span〉 from 〈span〉C〈/span〉2/〈span〉m〈/span〉 to 〈span〉C〈/span〉2 comes from the short-range bond-valence requirements of the structure.〈/span〉
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  • 9
    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉Laverovite (IMA 2017-009b), ideally K〈sub〉2〈/sub〉NaMn〈sub〉7〈/sub〉Zr〈sub〉2〈/sub〉(Si〈sub〉4〈/sub〉O〈sub〉12〈/sub〉)〈sub〉2〈/sub〉O〈sub〉2〈/sub〉(OH)〈sub〉4〈/sub〉F, is a kupletskite-group (astrophyllite-supergroup) mineral from Mont Saint-Hilaire, Québec, Canada. Associated minerals are zircophyllite, kupletskite, astrophyllite, aegirine, analcime, orthoclase, and albite. Laverovite is brown, transparent in thin grains, and has a vitreous luster. Mohs hardness is 3, 〈span〉D〈/span〉〈sub〉calc.〈/sub〉 = 3.367 g/cm〈sup〉3〈/sup〉. Laverovite is biaxial (–) with refractive indices (λ = 589 nm) α = 1.670(2), β = 1.710(5), γ = 1.740(5); 2〈span〉V〈/span〉〈sub〉meas.〈/sub〉 = 82(2)°, 2〈span〉V〈/span〉〈sub〉calc.〈/sub〉 = 80°, strong dispersion: 〈span〉r〈/span〉 〉 〈span〉v〈/span〉. Cleavage is perfect parallel to {001}. Chemical analysis by electron microprobe gave Nb〈sub〉2〈/sub〉O〈sub〉5〈/sub〉 0.56, ZrO〈sub〉2〈/sub〉 9.78, TiO〈sub〉2〈/sub〉 4.69, SiO〈sub〉2〈/sub〉 33.52, Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉 0.94, SrO 0.13, ZnO 0.07, FeO 13.94, MnO 20.51, CaO 0.48, MgO 0.76, Cs〈sub〉2〈/sub〉O 0.05, K〈sub〉2〈/sub〉O 6.00, Na〈sub〉2〈/sub〉O 2.28, F 1.80, H〈sub〉2〈/sub〉O〈sub〉calc.〈/sub〉 2.57, sum 97.32 wt.%; H〈sub〉2〈/sub〉O was calculated from crystal-structure analysis. The empirical formula based on 31.15 (O + F) 〈span〉apfu〈/span〉 with [OH + F = 5 〈span〉pfu〈/span〉 and H〈sub〉2〈/sub〉O = 0.15 〈span〉pfu〈/span〉] is (K〈sub〉1.78〈/sub〉Sr〈sub〉0.02〈/sub〉Cs〈sub〉0.01〈/sub〉□〈sub〉0.19〈/sub〉)〈sub〉Σ2〈/sub〉(□〈sub〉1.85〈/sub〉Na〈sub〉0.15〈/sub〉)〈sub〉Σ2〈/sub〉(Na〈sub〉0.88〈/sub〉Ca〈sub〉0.12〈/sub〉)〈sub〉Σ1〈/sub〉(Mn〈sub〉4.03〈/sub〉Fe〈sup〉2+〈/sup〉〈sub〉2.71〈/sub〉Mg〈sub〉0.25〈/sub〉Zn〈sub〉0.01〈/sub〉)〈sub〉Σ7〈/sub〉(Zr〈sub〉1.11〈/sub〉Ti〈sub〉0.82〈/sub〉Nb〈sub〉0.06〈/sub〉Mg〈sub〉0.01〈/sub〉)〈sub〉Σ2〈/sub〉[(Si〈sub〉7.78〈/sub〉Al〈sub〉0.26〈/sub〉)〈sub〉Σ8.04〈/sub〉O〈sub〉24〈/sub〉]O〈sub〉2〈/sub〉[(OH)〈sub〉3.68〈/sub〉F〈sub〉0.32〈/sub〉]〈sub〉Σ4〈/sub〉F[□〈sub〉1.85〈/sub〉(H〈sub〉2〈/sub〉O)〈sub〉0.15〈/sub〉]〈sub〉Σ2〈/sub〉, 〈span〉Z〈/span〉 = 1. The simplified formula is K〈sub〉2〈/sub〉Na(Mn,Fe〈sup〉2+〈/sup〉)〈sub〉7〈/sub〉(Zr,Ti)〈sub〉2〈/sub〉(Si〈sub〉4〈/sub〉O〈sub〉12〈/sub〉)〈sub〉2〈/sub〉O〈sub〉2〈/sub〉 (OH)〈sub〉4〈/sub〉F. Laverovite is triclinic, space group 〈span〉P〈/span〉, 〈span〉a〈/span〉 5.4329(1), 〈span〉b〈/span〉 11.9232(3), 〈span〉c〈/span〉 11.7491(3) Å, α 112.905(2), β 94.696(1), γ 103.178(1)°, 〈span〉V〈/span〉 670.14(5) Å〈sup〉3〈/sup〉. The six strongest lines in the X-ray powder diffraction data [〈span〉d〈/span〉 (Å)(I)(〈span〉hkl〈/span〉)] are: 3.452(92)(003,111); 2.788(97); 2.680(68); 2.589(100); 2.504(44), and 1.590(50). The crystal structure has been refined to 〈span〉R〈/span〉〈sub〉1〈/sub〉 = 3.26% for 3757 observed (〈span〉F〈/span〉〈sub〉o〈/sub〉 〉 4σ〈span〉F〈/span〉) reflections. In the crystal structure of laverovite, there are four 〈sup〉[4]〈/sup〉〈span〉T〈/span〉 sites, with 〈T–O〉 = 1.621 Å, occupied mainly by Si, with minor Al. TO〈sub〉4〈/sub〉 tetrahedra constitute the T〈sub〉4〈/sub〉O〈sub〉12〈/sub〉 astrophyllite ribbon. The Zr-dominant 〈sup〉[6]〈/sup〉〈span〉D〈/span〉 site is occupied mainly by Zr and Ti and minor Nb and Mg, with 〈D–φ〉 = 2.002 Å (φ = O, F). The T〈sub〉4〈/sub〉O〈sub〉12〈/sub〉 astrophyllite ribbons and D octahedra constitute the H (Heteropolyhedral) sheet. In the O (Octahedral) sheet, there are four Mn〈sup〉2+〈/sup〉-dominant 〈sup〉[6]〈/sup〉〈span〉M〈/span〉(1–4) sites, with 〈M(1–4)–φ〉 = 2.187, 2.174, 2.161, and 2.146 Å (φ = O, OH). Two H sheets and the central O sheet form the HOH block, and adjacent HOH blocks link 〈span〉via〈/span〉 a common X〈span〉P〈/span〉〈sub〉D〈/sub〉 anion of two D octahedra. In the 〈strong〉I〈/strong〉 (Intermediate) block between adjacent HOH blocks, there are two interstitial cation sites, 〈span〉A〈/span〉 and 〈span〉B〈/span〉, and a 〈span〉W〈/span〉〈sub〉A〈/sub〉 site, partly occupied by H〈sub〉2〈/sub〉O. The 〈span〉A〈/span〉 site splits into two partly occupied sites, 〈sup〉[13]〈/sup〉〈span〉A〈/span〉(1) and 〈sup〉[6]〈/sup〉〈span〉A〈/span〉(2), with A(1)–A(2) = 1.108 Å. The 〈sup〉[13]〈/sup〉〈span〉A〈/span〉(1) site is occupied at 90.5%: mainly by K, with minor Sr and Cs, 〈A(1)–φ〉 = 3.326 Å; the 〈sup〉[6]〈/sup〉〈span〉A〈/span〉(2) site is occupied at 7.5% by Na: [□〈sub〉1.85〈/sub〉Na〈sub〉0.15〈/sub〉], 〈A(2)–φ〉 = 2.29 Å (φ = O, F, H〈sub〉2〈/sub〉O). The aggregate content of the 〈span〉A〈/span〉 site is (K〈sub〉1.78〈/sub〉Sr〈sub〉0.02〈/sub〉Cs〈sub〉0.01〈/sub〉Na〈sub〉0.15〈/sub〉□〈sub〉0.04〈/sub〉)〈sub〉Σ2〈/sub〉, ideally K〈sub〉2〈/sub〉〈span〉apfu〈/span〉. The 〈sup〉[10]〈/sup〉〈span〉B〈/span〉 site is occupied by (Na〈sub〉0.88〈/sub〉Ca〈sub〉0.12〈/sub〉), 〈〈span〉B〈/span〉–φ〉 = 2.646 Å. The 〈span〉W〈/span〉〈sub〉A〈/sub〉 site is occupied at 7.5% by H〈sub〉2〈/sub〉O: [□〈sub〉1.85〈/sub〉(H〈sub〉2〈/sub〉O)〈sub〉0.15〈/sub〉] 〈span〉pfu〈/span〉. The presence of OH and H〈sub〉2〈/sub〉O groups in the laverovite structure was confirmed by infrared spectroscopy. The mineral is named “laverovite” after Professor Nikolay Pavlovich Laverov (1930–2016), Academician of the Russian Academy of Sciences, a prominent Russian ore geologist and an expert in uranium ore deposits and radiogenic waste disposal. Laverovite is a Mn-analogue of zircophyllite, K〈sub〉2〈/sub〉NaFe〈sup〉2+〈/sup〉〈sub〉7〈/sub〉Zr〈sub〉2〈/sub〉(Si〈sub〉4〈/sub〉O〈sub〉12〈/sub〉)〈sub〉2〈/sub〉O〈sub〉2〈/sub〉(OH)〈sub〉4〈/sub〉F. 〈/span〉
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    Electronic ISSN: 1499-1276
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  • 10
    Publication Date: 2017-06-27
    Description: Here we report the crystal structure of zircophyllite, ideally K 2 NaFe 2+ 7 Zr 2 (Si 4 O 12 ) 2 O 2 (OH) 4 F, from Mont Saint-Hilaire, Québec, Canada. This is the first determination of the crystal structure of zircophyllite, which was originally described by Kapustin (1972) . Zircophyllite is a mineral of the astrophyllite group of the astrophyllite supergroup. Chemical analysis by electron microprobe gave SiO 2 31.89, Al 2 O 3 1.54, Na 2 O 1.91, K 2 O 6.13, Rb 2 O 0.19, Cs 2 O 0.10, CaO 0.62, SrO 0.10, MgO 0.22, ZnO 0.48, FeO 17.60, MnO 17.19, TiO 2 4.48, ZrO 2 8.65, Nb 2 O 5 2.07, F 1.36, (H 2 O) calc. 2.53, sum 96.48 wt.%; H 2 O was calculated from crystal-structure analysis. The empirical formula based on 31 (O + F) pfu is (K 1.85 Rb 0.03 Cs 0.01 Na 0.05 ) 1.94 (Na 0.83 Ca 0.16 Sr 0.01 ) 1 (Fe 2+ 3.48 Mn 3.44 Zn 0.08 Mg 0.08 ) 7.09 (Zr 1.00 Ti 0.80 Nb 0.22 ) 2.02 [(Si 7.54 Al 0.43 ) 7.97 O 24 ]O 2 [(OH) 3.98 F 0.02 ] 4 F, Z = 1, D calc. = 3.365 g/cm 3 . Zircophyllite is triclinic, space group P , a 5.447(2), b 11.966(5), c 11.789(4) Å, α 112.95(1), β 94.688(6), 103.161(7)°, V 676.4(7) Å 3 . The crystal structure has been refined from a twinned crystal to R 1 = 3.79% for 3657 unique ( F o 〉 4 F ) reflections. In the crystal structure of zircophyllite, the four [4] T sites, with 〈T–O〉 = 1.626 Å, are occupied mainly by Si, with minor Al. The [6] D site is occupied by Zr 1.00 Ti 0.78 Nb 0.20 , ideally Zr 2 apfu , with 〈D–〉 = 2.013 Å ( = O, F). The T 4 O 12 astrophyllite ribbons and D octahedra constitute the H (Heteropolyhedral) sheet. In the O (Octahedral) sheet, the four [6] M (1–4) sites, with 〈M–〉 = 2.173 Å ( = O, OH), are occupied by (Fe 2+ 3.48 Mn 3.44 Zn 0.04 Mg 0.04 ), ideally Fe 2+ 7 apfu . The central O sheet and two H sheets form the HOH block, and adjacent HOH blocks link via a common anion (X P D = F) of two D octahedra. In the I (Intermediate) block between adjacent HOH blocks, the two interstitial cation sites, [13] A and [10] B , are ideally occupied by K 2 and Na apfu , 〈A–〉 = 3.338 Å and 〈B–〉 = 2.650 Å ( = O, F). Zircophyllite is a Zr-analogue of astrophyllite, K 2 NaFe 2+ 7 Ti 2 (Si 4 O 12 ) 2 O 2 (OH) 4 F. Zircophyllite and astrophyllite are related by the substitution: D Zr 4+ D Ti 4+ .
    Print ISSN: 0008-4476
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