Uvite, CaMg3(Al5Mg)(Si6O18)(BO3)3(OH)3(OH), a new, but long-anticipated mineral species of the tourmaline supergroup from San Piero in Campo, Elba Island, Italy

Uvite, CaMg3(Al5Mg)(Si6O18)(BO3)(3)(OH)(3)(OH), is a new mineral of the tourmaline supergroup. It occurs in the Facciatoia quarry, San Piero in Campo, Elba Island, Italy (42 degrees 45' 04.55 '' N, 10 degrees 12'50.89 '' E) at the centre of a narrow (2-3 cm wide) vein composed of aggregates of dark brown to black tourmaline, penetrating (magnesite + dolomite)-rich hydrothermally altered metaserpentinite. Crystals are euhedral and up to 1 cm in size, brown with a vitreous lustre, conchoidal fracture and grey streak. Uvite has a Mohs hardness of similar to 7 1/2, a calculated density of 3.115 g/cm(3) and is uniaxial (-). Uvite has trigonal symmetry, space group R3m, a = 15.9519(10) angstrom, c = 7.2222(5) angstrom, V = 1597.3(1) angstrom 3 and Z = 3. The crystal structure was refined to R-1 = 1.77% using 1666 unique reflections collected with MoKa X-rays. Crystal-chemical analysis resulted in the empirical crystal-chemical formula (X)(Ca(0.61)Na(0.35)A(0.04)) S1.00Y Mg1.50Fe0.472+Al0.71Fe3+similar to 0.14Ti(0.1)8 similar to S3.00 Z Al4.54Fe0.183+V3+similar to 0.02 Mg-1.27) S-6.00 T Si5.90Al0.10()similar to S6.00O18 similar to BO3() 3O(3)(OH) 3O(1)[(OH)(0.55)F0.05O0.40] S1.00which recast in its ordered form for classification purposes is:Uvite is a hydroxy-species belonging to the calcic-group of the tourmaline supergroup. The closest end-member compositions of valid tourmaline species are fluor-uvite and feruvite, to which uvite is related by the substitutions W(OH)-. WF- and YMg2+. YFe2+, respectively. The occurrence of a solid-solution between uvite and magnesio-lucchesiite, according to the substitution ZMg2+ + W(OH)-. ZAl(3+) + WO2-, is supported by experimental data. The new mineral was approved by the IMA-CNMNC (IMA 2019-113). Uvite from Facciatoia formed by the reaction between B-rich fluids, released during the crystallisation process of LCT pegmatites, and the surrounding metaserpentinites, altered by contact metamorphism in the aureole of the Miocene Mt. Capanne monzogranitic pluton.