IMA 2014-098 = fogoite-(Y)

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Marco E. Ciriotti
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Iscritto il: ven 25 giu, 2004 11:31
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IMA 2014-098 = fogoite-(Y)

Messaggio da Marco E. Ciriotti » gio 05 mag, 2016 16:27

Referenza:
▪ Cámara, F., Sokolova, E., Abdu, Y.A., Hawthorne, F.C., Charrier, T., Dorcet, V., Carpentier, J.-F. (2017): Fogoite-(Y), Na3Ca2Y2Ti(Si2O7)2OF3, a Group-I TS-block mineral from the Lagoa do Fogo, the Fogo volcano, the São Miguel Island, the Azores: Description and crystal structure. Mineralogical Magazine, 81, (in press).

Abstract:
Fogoite-(Y), Na3Ca2Y2Ti(Si2O7)2OF3, is a new mineral from the Lagoa do Fogo, the São Miguel Island, the Azores. It occurs in cavities as highly elongated (on [001]) prisms, up to 2000 μm long and 50 x 50 μm in cross-section, associated to sanidine, astrophyllite, fluornatropyrochlore, ferrokentbrooksite, quartz and ferro-katophorite. Crystals are generally transparent and colourless, with vitreous luster, occasionally creamy white. Fogoite-(Y) has a white streak, splintery fracture and very good {100} cleavage. Mohs hardness is ~5. Dcalc. = 3.523 g/cm3. It is biaxial (+) with refractive indices (λ = 590 nm) α = 1.686(2), β = 1.690(2), γ = 1.702(5); 2Vmeas.= 57(1)° and 2Vcalc. = 60°. It is nonpleochroic. Fogoite-(Y) is triclinic, space group P1-, a = 9.575(6), b = 5.685(4), c = 7.279(5) Å, α = 89.985(6), β = 100.933(4), γ = 101.300(5)°, V = 381.2(7) Å3. The six strongest reflections in the X-ray powder diffraction data [d (Å), I, (h k l)] are: 2.954, 100, (⎯1⎯1 2,⎯3 1 0); 3.069, 42, (3 0 0, 0⎯1 2); 2.486, 24, (3 1 0, 2⎯1 2); 3.960, 23, (⎯1⎯1 1,⎯2 1 0); 2.626, 21, (⎯2 2 0); 1.820, 20, (⎯1 0 4). Electron microprobe analysis gave the following empirical formula calculated on 18 (O + F) (Na2.74Mn0.15)Σ2.89Ca2[Y1.21(La0.01Ce0.03.03Sm0.02Gd0.08Dy0.08Er0.05Yb0.04Lu0.01)Σ0.35Mn0.16Zr0.11Na0.09Fe2+0.07Ca0.01]Σ2(Ti0.76Nb 0.23Ta0.01)Σ1(Si4.03O14)O1.12F2.88, Z = 1. The crystal structure was refined on a twinned crystal to R1 = 2.81% on the basis of 2157 unique reflections (Fo > 4σFo) and is a framework of TS (Titanium Silicate) blocks, which consists of HOH sheets (H-heteropolyhedral, O-octahedral) parallel to (100). In the O sheet, the the [6]MO(1) site is occupied mainly by Ti, = 1.980 Å and the [6]MO(2) and [6]MO(3) sites are occupied by Na and Na plus minor Mn, = 2.490 Å and = 2.378 Å. In the H sheet, the two [4]Si sites are occupied by Si, with = 1.623 Å; the [6]MH site is occupied by Y and REE (Y > REE), with minor Mn, Zr, Na, Fe2+ and Ca, = 2.271 Å and the [6]AP site is occupied by Ca, = 2.416 Å. The MH and AP octahedra and Si2O7 groups constitute the H sheet. The ideal compositions of the O and two H sheets are Na3Ti(OF)F2 and Y2Ca2(Si2O7)2 a.p.f.u. Fogoite-(Y) is isostructural with götzenite. The mineral is named after the type locality, the Fogo volcano in the Azores.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

Avatar utente
Marco E. Ciriotti
Messaggi: 23405
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
Contatta:

Re: IMA 2014-098 = fogoite-(Y)

Messaggio da Marco E. Ciriotti » gio 30 mar, 2017 12:01

Pubblicazione effettuata.

Referenza:
▪ Cámara, F., Sokolova, E., Abdu, Y.A., Hawthorne, F.C., Charrier, T., Dorcet, V., Carpentier, J.-F. (2017): Fogoite-(Y), Na3Ca2Y2Ti(Si2O7)2OF3, a Group-I TS-block mineral from the Lagoa do Fogo, the Fogo volcano, the São Miguel Island, the Azores: Description and crystal structure. Mineralogical Magazine, 81, 369–381.
Marco E. Ciriotti

«Things are interesting only in so far as they relate themselves to other things»

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