Elbaite, the neotype material from the Rosina pegmatite, San Piero in Campo, Elba island, Italy

Abstract

Elbaite, Na(Li1.5Al1.5)Al6(Si6O18)(BO3)3(OH)3(OH), is a mineral species of the tourmaline supergroup. A formal description of the neotype elbaite material, approved by the International Mineralogical Association's Commission on New Minerals, Nomenclature and Classification (IMA-CNMNC), is presented in this study. Elbaite occurs in the Rosina pegmatite, San Piero in Campo, Elba island, Italy (42°44′51.35′′ N, 10°12′38.02′′ E). Crystals show euhedral habitus, are up to 1.5 cm in length, and are colorless with a vitreous luster, conchoidal fracture, and white streak. Elbaite has a Mohs hardness of approximately 7, has a calculated density of 3.04 g cm−3, and is uniaxial negative. It has trigonal symmetry, space group R3m, a=15.8117(2) Å, c=7.0937(1) Å, V=1535.89(4) Å3, and Z=3. The crystal structure was refined to R1=2.12 % using 1783 unique reflections collected with MoKα X-ray intensity data. Crystal–chemical analysis resulted in the empirical formula X(Na0.71□0.28Ca0.01)Σ1.00Y(Al1.77Li1.16Mn0.062+Fe0.012+)Σ3.00ZAl6.00[T(Si5.94B0.06)Σ6.00O18](BO3)3V(OH)3W[(OH)0.48F0.23O0.29]Σ1.00. The neotype elbaite originates from a nearly colorless crystal with a black to dark-green base. Chemical analysis shows a transition from Mn-rich schorl in darker areas to chemically homogeneous elbaite in lighter regions, with Fe and Mn contents decreasing significantly due to a (Li + Al) substitution. In the Rosina pegmatite, tourmaline is the primary boron mineral, increasing in abundance toward the core. Its composition reflects the pegmatite's geochemical evolution, with rising Li and Cs contents in deeper zones. Early crystallization of biotite, sekaninaite, and Fe-rich schorl removed Mg, Ti, and Fe from the system, allowing later-stage tourmaline to evolve into Fe-free, Mn-rich fluor-elbaite. The present elbaite crystals formed in cavities in the pegmatite's deeper sections. Low Mn and F contents resulted from spessartine and lepidolite crystallization, respectively. As a result, tourmaline near cavities evolved into homogeneous, nearly colorless elbaite prisms.