Princivalleite, Na(Mn₂Al)Al₆(Si₆O₁₈)(BO₃)₃(OH)₃O, a new mineral species of the tourmaline supergroup from Veddasca Valley, Varese, Italy

Abstract Princivalleite, Na(Mn 2 Al)Al 6 (Si O 18 )(BO 3 ) (OH) O, is a new mineral (IMA2020-056) of the tourmaline supergroup. It occurs in Veddasca Valley, Luino area, Varese, Lombardy, Italy (46°03’30.74’’N, 8°48’24.47’’E) at centre narrow (2–3 cm wide) vertical pegmatitic vein, few metres long, crosscutting lens flaser gneiss. Crystals are subhedral (up to 10 mm size), azure with vitreous lustre, conchoidal fracture and white streak. Princivalleite has Mohs hardness ~7, calculated density 3.168 g/cm uniaxial (–). trigonal symmetry, space group R m , = 15.9155(2) Å, c 7.11660(10) V 1561.15(4) Å Z 3. The crystal structure was refined 1 1.36% using 1758 unique reflections collected Mo K ? X-ray intensity data. Crystal-chemical analysis resulted empirical crystal-chemical formula X (Na 0.54 Ca 0.11 ? 0.35 ?1.00 Y (Al 1.82 Mn 2+ 0.84 Fe 0.19 Zn 0.07 Li 0.08 ?3.00 5.85 0.13 Mg 0.02 ?6.00 [ T 5.60 Al 0.40 ](BO O(3) [(OH) 2.71 0.29 ] O(1) [O 0.66 F 0.22 0.12 which recast its ordered form for classification purposes is: 1.67 0.32 6.00 W . an oxy-species belonging alkali closest end-member compositions valid species those oxy-schorl darrellhenryite, princivalleite related by substitutions ? 0.5Al 3+ + 0.5Li respectively. from Valley geochemical anomaly, originated B-rich peraluminous anatectic melt formed situ poor characterised reducing conditions late-stage metamorphic fluids derived Mn-enrichment this due absence other minerals competing such as garnet.