Tourmaline crystals from the island of Elba commonly display a sharp transition to dark colors at the analogous termination due to the incorporation of Fe and/or Mn during the latest stages of crystallization in pegmatites. The formation of such color anomalies is related to a dramatic physicochemical change in the crystallization environment as a consequence of an opening of the geochemical system. However, mechanisms that may lead to the availability of Fe and/or Mn in the residual cavity fluids have been unclear. On the basis of chemical and spectroscopic investigations, combined with structural and paragenetic observations of the cavities, we propose a general genetic model in which, as a consequence of a pocket rupture event, chemical alteration of Fe- and Mn-rich minerals that formed early in the pegmatitic rock surrounding the cavities occurred through leaching processes, produced by the action of the highly reactive late-stage cavity fluids. Such processes were responsible for the release of Fe and Mn in the geochemical system, allowing the formation of the late-stage dark-colored terminations in the tourmaline crystals. In some cavities, a high availability of Mn and/or Fe determined the evolution of the crystals from an initial elbaite/fluor-elbaite composition to celleriite, foitite or schorl. This compositional evolution trend can be described by the following general chemical substitution: XNa+ + Y(Li1.5 + Al0.5)3+ + WF− ↔ X□ + 2Y(Fe,Mn)2+ + WOH−.

Genetic model for the color anomalies at the termination of pegmatitic gem tourmaline crystals from the island of Elba, Italy / Altieri, Alessandra; Pezzotta, Federico; Andreozzi, Giovanni B.; Skogby, Henrik; Bosi, Ferdinando. - In: EUROPEAN JOURNAL OF MINERALOGY. - ISSN 1617-4011. - 35:5(2023), pp. 755-771. [10.5194/ejm-35-755-2023]

Genetic model for the color anomalies at the termination of pegmatitic gem tourmaline crystals from the island of Elba, Italy

Alessandra Altieri
;
Giovanni B. Andreozzi;Ferdinando Bosi
2023

Abstract

Tourmaline crystals from the island of Elba commonly display a sharp transition to dark colors at the analogous termination due to the incorporation of Fe and/or Mn during the latest stages of crystallization in pegmatites. The formation of such color anomalies is related to a dramatic physicochemical change in the crystallization environment as a consequence of an opening of the geochemical system. However, mechanisms that may lead to the availability of Fe and/or Mn in the residual cavity fluids have been unclear. On the basis of chemical and spectroscopic investigations, combined with structural and paragenetic observations of the cavities, we propose a general genetic model in which, as a consequence of a pocket rupture event, chemical alteration of Fe- and Mn-rich minerals that formed early in the pegmatitic rock surrounding the cavities occurred through leaching processes, produced by the action of the highly reactive late-stage cavity fluids. Such processes were responsible for the release of Fe and Mn in the geochemical system, allowing the formation of the late-stage dark-colored terminations in the tourmaline crystals. In some cavities, a high availability of Mn and/or Fe determined the evolution of the crystals from an initial elbaite/fluor-elbaite composition to celleriite, foitite or schorl. This compositional evolution trend can be described by the following general chemical substitution: XNa+ + Y(Li1.5 + Al0.5)3+ + WF− ↔ X□ + 2Y(Fe,Mn)2+ + WOH−.
2023
tourmaline-supergroup minerals; electron microprobe; Mössbauer spectroscopy; gem-pegmatites; pocket-rupture; crystal growth
01 Pubblicazione su rivista::01a Articolo in rivista
Genetic model for the color anomalies at the termination of pegmatitic gem tourmaline crystals from the island of Elba, Italy / Altieri, Alessandra; Pezzotta, Federico; Andreozzi, Giovanni B.; Skogby, Henrik; Bosi, Ferdinando. - In: EUROPEAN JOURNAL OF MINERALOGY. - ISSN 1617-4011. - 35:5(2023), pp. 755-771. [10.5194/ejm-35-755-2023]
File allegati a questo prodotto
File Dimensione Formato  
Altieri_Genetic_2023.pdf

accesso aperto

Note: Articolo
Tipologia: Versione editoriale (versione pubblicata con il layout dell'editore)
Licenza: Creative commons
Dimensione 727.2 kB
Formato Adobe PDF
727.2 kB Adobe PDF

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/1688418
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 2
  • ???jsp.display-item.citation.isi??? ND
social impact