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Article
Geologica Carpathica, 2025, vol. 76, no. 4
Different crystallization events of Li-bearing pegmatitic tourmaline from San Piero in Campo, Elba Island, Italy
Abstract
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.
Keywords:
tourmaline, zonation, pegmatite pockets, crystallization events, Rosina aplite-pegmatite, Monte Capanne pluton
Pages:
301 - 309
Published online:
6 November 2025