Crystal-chemistry of Y-poor hainite-(Y) from Poços de Caldas alkaline complex, Minas Gerais, Brazil

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Marco E. Ciriotti
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Crystal-chemistry of Y-poor hainite-(Y) from Poços de Caldas alkaline complex, Minas Gerais, Brazil

Messaggio da Marco E. Ciriotti » mer 15 ago, 2018 10:25

Referenza:
▪ Azzi, A., Atencio, D., Andrade, M., Reynaldo Contreira, R. (2018): Crystal-chemistry of Y-poor hainite-(Y) from Poços de Caldas alkaline complex, Minas Gerais, Brazil. IMA2018 Abstract book. Mineralogical crystallography, 226.

Abstract:
Hainite was originally described by Blumrich (1893) in cavities and groundmass of phonolites and tinguaites from Hradiste, Czech Republic, and named on the basis of incomplete optical and qualitative chemical data. Complete chemical analysis and X-ray powder-diffraction data were published later by Johan & Čech (1989). A second occurrence of hainite has been established also in cavities and groundmass of evolved rocks (nepheline syenites and tinguaites) in the alkaline massif of Poços de Caldas, Minas Gerais state, Brazil (Atencio et al., 1999). Since the formula Ca4Na(NaCa)Ti(Si2O7)2(OF2)F2 is not electronically neutral, Sokolova and Cámara (2017) have modified it for (Ca3Y)Na(NaCa)Ti(Si2O7)2(OF2)F2 and changed the name to hainite-(Y). Rare-earth elements are chemically essential constituents and need to have their own position in the mineral formula to keep neutral-charge stoichiometry. According to Sokolova and Cámara (2017) the Levinson suffix should be applied to a mineral with Y and/or lanthanoids (Ln: La–Lu) regardless of whether Y and/or lanthanoids are dominant at particular crystallographic sites. Consequently, the new name and formula should be applied for both the Y-rich hainite-(Y) from Russia and the Y-poor hainite-(Y) from Poços de Caldas. A total of 56 new analyses made possible a series of calculation and atoms distribution in the structural sites. Hainite-(Y) specimens from Poços de Caldas have 0.01 to 0.03 Y apfu. Interesting fact about the hainite crystals from Poços de Caldas is the minerals occurring as inclusions in cavities of dissolution (Fig.1). Minerals such as pectolite, rinkite-(Ce), fluorapatite, stronadelphite and members of the britholite group, some of them new minerals under study. Other associated minerals are villiaumite, fluorite, manganoeudialyte, natrolite, aegirine, lorenzenite, batisite, chlorbartonite, tuppersuatsiaite, astrophyllite, lamprophyllite, gaidonnayite, pyrophanite, vishnevite, sodalite, pyrite, polezhaevaite, ferrobustamite, vinogradovite, burbankite, ancylite-(Ce) and ancylite-(La).
Marco E. Ciriotti

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