Two tourmaline crystals with a blue growth zone at the analogous pole, respectively from the San Silvestro and the Fucili pegmatites, located in the San Piero in Campo village, Elba Island (Tyrrhenian Sea, Italy), have been described for the first time using compositional and spectroscopic data to define their crystal-chemical aspects and the causes of the colour. Compositional data obtained by electron microprobe analysis indicate that both tourmalines belong to the elbaite–fluor-elbaite series. The upper part of each crystal is characterised by an increased amount of Fe (FeO up to ~1 wt.%) and a Ti content below the detection limit. Optical absorption spectra recorded on the blue zone of both samples show absorption bands caused by spin-allowed d-d transitions in [6]-coordinated Fe2+, and no intervalence charge transfer Fe2+-Ti interactions, indicating that Fe2+ is the only chromophore. Mössbauer analysis of the blue zone of the Fucili sample confirmed the Fe2+ oxidation state, implying that the redox conditions in the crystallisation environment were relatively reducing. The presence of colour changes at the analogous termination during tourmaline crystal growth suggests a change in the composition of the crystallisation environment, probably associated with a partial opening of the system.

Blue-growth zones caused by Fe2+ in tourmaline crystals from the San Piero in Campo gem-bearing pegmatites, Elba Island, Italy / Altieri, Alessandra; Pezzotta, Federico; Skogby, Henrik; H(aa)lenius, Ulf; Bosi, Ferdinando. - In: MINERALOGICAL MAGAZINE. - ISSN 0026-461X. - 86:(2022), pp. 910-919. [10.1180/mgm.2022.101]

Blue-growth zones caused by Fe2+ in tourmaline crystals from the San Piero in Campo gem-bearing pegmatites, Elba Island, Italy

Alessandra Altieri
Primo
;
Ferdinando Bosi
2022

Abstract

Two tourmaline crystals with a blue growth zone at the analogous pole, respectively from the San Silvestro and the Fucili pegmatites, located in the San Piero in Campo village, Elba Island (Tyrrhenian Sea, Italy), have been described for the first time using compositional and spectroscopic data to define their crystal-chemical aspects and the causes of the colour. Compositional data obtained by electron microprobe analysis indicate that both tourmalines belong to the elbaite–fluor-elbaite series. The upper part of each crystal is characterised by an increased amount of Fe (FeO up to ~1 wt.%) and a Ti content below the detection limit. Optical absorption spectra recorded on the blue zone of both samples show absorption bands caused by spin-allowed d-d transitions in [6]-coordinated Fe2+, and no intervalence charge transfer Fe2+-Ti interactions, indicating that Fe2+ is the only chromophore. Mössbauer analysis of the blue zone of the Fucili sample confirmed the Fe2+ oxidation state, implying that the redox conditions in the crystallisation environment were relatively reducing. The presence of colour changes at the analogous termination during tourmaline crystal growth suggests a change in the composition of the crystallisation environment, probably associated with a partial opening of the system.
2022
tourmaline; electron microprobe; optical absorption spectroscopy; infrared spectroscopy; petrogenetic indicator; growth history; miarolitic cavities; Elba Island
01 Pubblicazione su rivista::01a Articolo in rivista
Blue-growth zones caused by Fe2+ in tourmaline crystals from the San Piero in Campo gem-bearing pegmatites, Elba Island, Italy / Altieri, Alessandra; Pezzotta, Federico; Skogby, Henrik; H(aa)lenius, Ulf; Bosi, Ferdinando. - In: MINERALOGICAL MAGAZINE. - ISSN 0026-461X. - 86:(2022), pp. 910-919. [10.1180/mgm.2022.101]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/1661822
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