Different crystallization events of Li-bearing pegmatitic tourmaline from San Piero in Campo, Elba Island, Italy

Autor(en)

Andreas Ertl, Federico Pezzotta, John M. Hughes, Hans-Peter Meyer, Thomas Ludwig, M. Darby Dyar, Gerald Giester, George R. Rossman

Abstrakt

To learn more about the growth zones of distinctly zoned tourmalines from the well-studied Rosina aplite–

pegmatite dike of the Monte Capanne pluton near San Piero in Campo, Elba Island, Italy, four tourmaline crystals rooted

in the pegmatitic rock and developed into three different small cavities, as well as one additional crystal growing frozen

in the pegmatitic rock, were chemically characterized. The light element contents and the unit cell parameters of the four

samples were also determined. Black Fe²⁺-rich tourmaline, grown directly within the pegmatite, with unit cell parameters

a = 15.97–15.98 Å, c = 7.15–7.16 Å, can be assigned to schorl and fluor-schorl with only 4 % Fe³⁺. The Fe content

decreases during crystallization, whereas Mn and F contents increase (up to 8 wt% MnO and 1.4 wt% F), forming

a growth sector of olive-green colour. Such olive-green tourmaline exhibits unit cell parameters of a = 15.87–15.94 Å,

c = 7.12–7.14 Å and can be assigned to fluor-tsilaisite and Mn²⁺-rich fluor-elbaite. Later, the Mn content decreases and

the Al and Li contents increase (up to 44 wt% Al₂O₃ and 1.7 wt% Li₂O). These zones can have Ga and Pb contents of up

to ~1100 and ~500 ppm, respectively. The colour of such tourmaline can be pale olive-green, pale pink, or colourless.

These crystal zones have unit cell parameters of a = 15.78–15.82 Å, c = 7.08–7.10 Å, and can be assigned to fluor-elbaite,

elbaite, rossmanite, and darrellhenryite. In the final stage of tourmaline crystallization, the F content in the investigated

crystal terminations can drop down to 0.1 wt% F, while the (Fe + Mn) content increases. Usually, these terminations can

be assigned to elbaite (a = 15.79–15.83 Å, c = 7.08–7.10 Å). When comparing the F content and the X-site charge (Na, Ca),

all zones grown in the pegmatite pocket, except for the termination, show a strong positive correlation for each crystal

examined. This observation is interpreted as evidence that the caps of the tourmaline crystals in the pegmatite pockets

formed during a different event than the previously grown crystals.

Organisation(en)

Institut für Mineralogie und Kristallographie

Externe Organisation(en)

MUM – Mineralogical Museum “Luigi Celleri”, Via Cavour 73, San Piero in Campo, Campo nell’Elba, 57034 (LI), Italy, University of Vermont, Universität Heidelberg, Planetary Science Institute, California Institute of Technology (Caltech)

Journal

Geologica Carpathica

Band

76

Seiten

301-309

Anzahl der Seiten

9

ISSN

1335-0552

DOI

https://doi.org/10.31577/GeolCarp.2025.18

Publikationsdatum

2025

Peer-reviewed

Ja

ÖFOS 2012

105116 Mineralogie, 105113 Kristallographie

Schlagwörter

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/27e5f200-8261-4214-b180-3045ba327ee0