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Formula: NaCaMn3+2(AsO4)2O(OH)
Arsenate, manganese-bearing mineral
Crystal System: Orthorhombic
Specific gravity: 4.084 calculated
Hardness: 5 to 5½
Streak: Brown
Colour: Black
Luminescence: Not fluorescent under UV
Environments
Piccoliite is a relatively new mineral, approved in 2017 and to date (May 2023) reported only from
type localities.
Localities
There are two co-type localities, the Valletta mine, Vallone della Valletta, Canosio, and the Montaldo Mine, Borgata
Oberti, Montaldo di Mondovì, both in Cuneo Province, Piedmont, Italy.
Piccoliite has been discovered at the Montaldo mine in the
iron-manganese ore hosted in
metaquartzite. It occurs as small and rare black crystals and
aggregates hosted by a matrix of quartz, associated with
calcite and
berzeliite/manganberzeliite.
It also has been found at the Valletta mine, where it occurs embedded in quartz
associated with grandaite,
hematite,
tilasite/adelite and rarely
thorianite. Piccoliite is opaque (thin splinters may be very dark
red), with a brown streak and a resinous to vitreous lustre
(MM 87.204-217).
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