Papagoite

Papagoite is a rare cyclosilicate mineral. Chemically, it is a calcium copper aluminium silicate hydroxide, found as a secondary mineral on slip surfaces and in altered granodiorite veins, either in massive form or as microscopic crystals that may form spherical aggregates. Its chemical formula is CaCuAlSi₂O₆(OH)₃.

Papagoite
Crystalline papagoite from Namibia (size: 5.9 x 3.3 x 2.1 cm)
General
Category	Cyclosilicate
Formula (repeating unit)	CaCuAlSi2O6(OH)3
Strunz classification	9.CE.05
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	C2/m
Unit cell	a = 12.92 Å, b = 11.49 Å, c = 4.69 Å; β = 100.81°; Z = 4
Identification
Color	Dark blue crystals, light blue when massive
Crystal habit	Massive; cryptocrystalline, forming flat elongated crystals
Cleavage	Imperfect in one direction
Fracture	Brittle
Mohs scale hardness	5-5.5
Luster	Vitreous to dull
Streak	Light blue
Specific gravity	3.25
Optical properties	Biaxial (-)
Refractive index	nα = 1.607 nβ = 1.641 nγ = 1.672
Birefringence	δ = 0.065
Pleochroism	Trichroic
2V angle	Measured: 78°
References	[1][2][3][4]

It was discovered in 1960 in Ajo, Arizona, US, and was named after the Hia C-ed O'odham people (also known as the Sand Papago) who inhabit the area.[4] This location is the only papagoite source within the United States, while worldwide it is also found in South Africa and Namibia. It is associated with aurichalcite, shattuckite, ajoite and baryte in Arizona, and with quartz, native copper and ajoite in South Africa.[4] Its bright blue color is the mineral's most notable characteristic.

It is used as a gemstone.[5]