Yukonite: studi strutturali e relazione con arsenosiderite

[Marco E. Ciriotti]

Referenza:
• Gomez, M.A., Becze, L., Blyth, R.I.R., Cutler, J.N., Demopoulos, G.P. (2010): Molecular and structural investigation of yukonite (synthetic & natural) and its relation to arseniosiderite. Geochimica et Cosmochimica Acta, 74, (in stampa).

Abstract:
This paper describes the first synthesis method of yukonite, its thorough molecular and structural analysis along with natural specimens originating from Tagish Lake (Canada) and Grotta della Monaca (Italy) for comparison, and its structural relation to arseniosiderite. The synthetic and natural yukonites were found to have a range of composition according to the general formula Ca2Fe3-5(AsO4)3(OH)4-10·xH2O where x = 2-11. The synthetic yukonite was found to be equivalent at the atomic, molecular and structural level to the Tagish Lake yukonite. At the molecular level, arseniosiderite, via vibrational spectroscopy, was found to have an H-bonding system as in scorodite and exhibit an extra arsenate mode indicative of HAsO42- groups. Heating experiments along with ATR-IR analysis indicated the presence of structural water and hydroxyl units in arseniosiderite. In yukonite in contrast, a wide diffuse H-bonding environment was observed with only arsenate groups. The presence of both structural water and hydroxyl groups was further verified via ATR-IR spectroscopy. The As K, Fe 2p and Ca 2p XANES spectra of yukonite and arseniosiderite are identical confirming that the local nature of the As, Fe and Ca atoms in these structures is the same. TEM and diffraction (X-ray and electron) showed that yukonite consists of nano-crystalline domains while in the case of arseniosiderite micro-size single crystal domains exist.