Formula: Na(Mn2Al)Al6(Si6O18)(BO3)(OH)3O
Cyclosilicate (ring silicate), borosilicate, tourmaline group, manganese-bearing mineral
Specific gravity: 3.168 calculated
Hardness: about 7
Streak: White
Colour: Azure


Princivalleite is a new mineral, approved in 2020, and to date (March 2022) reported only from the type locality.


At the type locality, Curiglia, Curiglia con Monteviasco, Varese Province, Lombardy, Italy, princivalleite occurs at the centre of a narrow (2–3 cm wide) vertical pegmatitic vein, a few metres long, crosscutting a lens of flaser gneiss. Crystals are subhedral, up to 10 mm in size.
Princivalleite is an oxy-species belonging to the alkali group of the tourmaline supergroup. The closest end-member compositions of valid tourmaline species are those of oxy-schorl and darrellhenryite. Princivalleite is a geochemical anomaly, originated in a boron-rich and peraluminous (aluminium-rich) anatectic (derived from melting of pre-existing rock) pegmatitic melt formed in situ, poor in iron and characterised by reducing conditions in the late-stage metamorphic fluids derived by the flaser gneiss. The manganese-enrichment in this new tourmaline is due to absence of other minerals competing for manganese, such as garnet (MM 86.78-86).

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