Dutrowite, Na(Fe2.52+Ti0.5)Al6(Si6O18)(BO3)3(OH)3O, a new mineral from the Apuan Alps (Tuscany, Italy). The first member of the tourmaline supergroup with Ti as a species-forming chemical constituent

The new tourmaline supergroup mineral dutrowite, Na(Fe2.52+Ti0.5)Al6(Si6O18)(BO3)3(OH)3O, has been discovered in an outcrop of a Permian metarhyolite near the hamlet of Fornovolasco, Apuan Alps, Tuscany, Italy. It occurs as chemically homogeneous domains, up to 0.5 mm, brown in colour, with a light-brown streak and a vitreous lustre, within anhedral to subhedral prismatic crystals, up to 1 mm in size, closely associated with Fe-rich oxy-dravite. Dutrowite is trigonal, space group R3m, with aCombining double low line15.9864(8), cCombining double low line7.2187(4) Å, VCombining double low line1597.68(18) Å3, and ZCombining double low line3. The crystal structure was refined to R1Combining double low line0.0257 for 1095 unique reflections with Fo>4σ (Fo) and 94 refined parameters. Electron microprobe analysis, coupled with Mössbauer spectroscopy, resulted in the empirical structural formula X(Na0.81Ca0.20K0.01)ς1.02 Y(Fe1.252+Mg0.76Ti0.56Al0.42)ς3.00 Z(Al4.71Fe0.273+V0.023+Mg0.82Fe0.182+)ς6.00 T[(Si5.82Al0.18)ς6.00O18] (BO3)3O(3)(OH)3O(1)[O0.59(OH)0.41]ς1.00, which was recast in the empirical ordered formula, required for classification purposes: X(Na0.81Ca0.20K0.01)ς1.02 Y(Fe1.432+Mg1.00Ti0.56)ς3.00 Z(Al5.13Fe0.273+V0.023+Mg0.58)ς6.00 T[(Si5.82Al0.18)ς6.00O18] (BO3)3V(OH)3 W[O0.59(OH)0.41]ς1.00. Dutrowite is an oxy-species belonging to the alkali group of the tourmaline supergroup. Titanium is hosted in octahedral coordination, and its incorporation is probably due to the substitution 2Al3+ Combining double low line Ti4+ + (Fe,Mg)2+. Its occurrence seems to be related to late-stage high-T/low-P replacement of "biotite"during the late-magmatic/hydrothermal evolution of the Permian metarhyolite.