IMA 2017-054 = baumoite

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Marco E. Ciriotti
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IMA 2017-054 = baumoite

Messaggio da Marco E. Ciriotti » dom 14 apr, 2019 12:04

Prossima pubblicazione.

Referenza:
▪ Elliott, P., Plášil, J., Petříček, V., Čejka, J., Bindi, L. (2019): Twinning and incommensurate modulation in baumoite, Ba0.5[(UO2)3O8Mo2(OH)3](H2O)∼3, the first natural Ba uranyl molybdate. Mineralogical Magazine, 83, (in press).

Abstract:
Baumoite, Ba0.5[(UO2)3O8Mo2(OH)3](H2O)~3, is a new mineral found near Radium Hill, South Australia, where it occurs in a granite matrix associated with barite, metatorbernite, phurcalite and kaolinite. Baumoite forms thin crusts of yellow to orange yellow tabular to prismatic crystals. The mineral is translucent with a vitreous lustre and pale yellow streak. Crystals are brittle, the fracture is uneven and show one excellent cleavage. The Mohs hardness is about 2½. The calculated density is 4.61 g/cm3. Optically, baumoite crystals are biaxial (-), with α = 1.716(4), β = 1.761(4), γ = 1.767(4) (white light); 2Vcalc = 42.2°. Electron microprobe analyses gave the empirical formula Ba0.87Ca0.03Al0.04U2.97Mo2.02P0.03O22H11.99, based on 22 O atoms per formula unit. The eight strongest lines in the X-ray powder diffraction pattern are [dobs Å (I) (hkl)]: 9.175 (39) (12-1), 7.450 (100) (020), 3.554 (20) (221), 3.365 (31) (004, 202), 3.255 (31) (123, 30-2), 3.209 (28) (12-4), 3.067 (33) (30-3, 222, 32-2) and 2.977 (20) (142). Single-crystal X-ray studies (R1 = 5.85% for 1892 main reflections) indicate that baumoite is monoclinic, superspace group X2/m(a0g)0s with X = (0,½,0,½), with unit-cell parameters: a = 9.8337(3), b = 15.0436(5), c = 14.2055(6) Å, beta = 108.978(3)°, V = 1987.25(13) Å3 and Z = 4. The crystal structure is twinned and incommensurately modulated and is based upon sheets of U6+ and Mo6+-polyhedra of unique topology. Four independent cationic sites partially occupied by Ba atoms are located between the sheets, together with H2O molecules.
Marco E. Ciriotti

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Marco E. Ciriotti
Messaggi: 25642
Iscritto il: ven 25 giu, 2004 11:31
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Re: IMA 2017-054 = baumoite

Messaggio da Marco E. Ciriotti » lun 15 apr, 2019 12:09

uranyl molybdates

Baumoite Ba(UO2)3(Mo2O)10(H2O)6
Calcurmolite (Ca,Na)2(UO2)3(MoO4)2(OH)3·10-15H2O
Cousinite MgU4+2[(MoO4)2(OH)6]·2H2O
Deloryite Cu4[(UO2)(MoO4)2(OH)6]
Iriginite [(UO2)Mo2O7(H2O)2]·H2O
Moluranite H4U4+[(UO2)3(MoO4)7]·18H2O
Sedovite U4+(MoO4)2
Tengchongite Ca[(UO2)6(MoO4)2O5]·12H2O
Umohoite [(UO2)(MoO4)H2O]·H2O

NdR: La struttura della baumoite non è troppo dissimile da quella di alcuni solfosali.
Marco E. Ciriotti

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