IMA 2021-096 = franksousaite

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Marco E. Ciriotti
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IMA 2021-096 = franksousaite

Messaggio da Marco E. Ciriotti » gio 28 lug, 2022 10:20

Referenza:
▪ Yang, H., McGlasson, J.A., Gibbs, R.B., Downs, R.T. (2022): Franksousaite, PbCu(Se6+O4)(OH)2, the Se6+ analogue of linarite, a new mineral from the El Dragón mine, Potosí, Bolivia. Mineralogical Magazine, 86, (in press).

Abstract:
A new mineral species, franksousaite (IMA 2021-096), ideally PbCu(Se6+O4)(OH)2, has been found from the El Dragón mine, Antonio Quijarro Province, Potosí Department, Bolivia. It occurs as short prismatic crystals included in colorless anglesite. Associated minerals are Co-bearing krutˊaite–penroseite, chalcomenite, schmiederite, olsacherite, phosgenite, anglesite, and cerussite. Franksousaite is blue in transmitted light, transparent with very pale blue streak and vitreous luster. It is brittle and has a Mohs hardness of 2-2½. Cleavage is perfect on {100}. The calculated density is 5.64 g/cm3. An electron microprobe analysis yielded an empirical formula (based on 6 O apfu) Pb1.02Cu0.98[(Se0.84S0.17)Σ1.01O4)](OH)2, which is simplified to PbCu[(Se,S)O4)](OH)2. Franksousaite is the Se6+ analogue of linarite, PbCu(SO4)(OH)2. It is monoclinic, with space group P21/m and unit-cell parameters a = 9.8208(3), b = 5.7340(2), c = 4.74980(10) Å, β = 102.683(2)°, V = 260.947(13) Å3, and Z = 2. The crystal structure of franksousaite consists of Jahn-Teller-distorted Cu2+O6 square bipyramids, which form chains along b by sharing trans edges across their square planes. The chains are decorated by SeO4 tetrahedra and linked to one another by hydrogen bonds to form layers parallel to (100). These layers are bound together by double layers of PbO8 and SeO4 polyhedra. The PbO8 polyhedron exhibits one-sided coordination typical of Pb2+ with a stereochemically active 6s2 lone-electron-pair. The major structural difference between franksousaite and linarite lies in the <Se-O> vs. <S-O> bond distances (1.615 vs. 1.482 Å), accounting for the larger unit-cell volume for franksousaite. A comparison of Raman spectra for the four minerals in the linarite group (linarite, franksousaite, munakataite, and schmiederite) reveals the obvious differences among them, especially in the range from 700 to 1000 cm-1, indicative of the presence or absence of (Se4+O3)2-, (Se6+O4)2-, and/or (SO4)2- groups.
Marco E. Ciriotti

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

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Marco E. Ciriotti
Messaggi: 31675
Iscritto il: ven 25 giu, 2004 11:31
Località: via San Pietro, 55 I-10073 Devesi/Cirié TO - Italy
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Re: IMA 2021-096 = franksousaite

Messaggio da Marco E. Ciriotti » mar 18 ott, 2022 10:36

Pubblicazione effettuata.

Referenza:
▪ Yang, H., McGlasson, J.A., Gibbs, R.B., Downs, R.T. (2022): Franksousaite, PbCu(Se6+O4)(OH)2, the Se6+ analogue of linarite, a new mineral from the El Dragón mine, Potosí, Bolivia. Mineralogical Magazine, 86, 792-798.
Marco E. Ciriotti

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

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