Gilalite

Gilalite is a copper silicate mineral with chemical composition of Cu₅Si₆O₁₇·7(H₂O).^[4]

Gilalite
Blue Gilalite crystals
General
Category	Silicate mineral
Formula	Cu5Si6O17·7(H2O)
IMA symbol	Gil[1]
Strunz classification	9.HE.05
Crystal system	Monoclinic Unknown space group
Unit cell	a = 13.38, b = 19.16 c = 9.026 [Å]; β ≈ 90°; Z = 4
Identification
Formula mass	884.3 g/mol
Color	Blue green, green
Crystal habit	Raidiating fibrous in spherules
Tenacity	Waxy or gummy
Mohs scale hardness	2
Luster	Nonmetallic
Streak	Light green
Diaphaneity	Translucent
Specific gravity	2.72
Optical properties	Biaxial (-)
Refractive index	nα= 1.560 nβ=1.635 nΎ= 1.635
Birefringence	δ = 0.075
References	[2][3][4]

It occurs as a retrograde metamorphic phase in a calc-silicate and sulfide skarn deposit. It occurs as fracture fillings and incrustations associated with diopside crystals.^[3] It is commonly found in the form of spherules of radial fibers.

Gilalite inclusions within a quartz crystal from Juazeiro do Norte, Ceara State, Brazil (size: 7.1 x 4.7 x 2.7 cm)

It was first described for an occurrence in the Christmas porphyry copper mine in Gila County, Arizona in 1980 along with the mineral apachite.^[5] It derives its name from this locality. It has also been reported from the Goodsprings District, Clark County, Nevada; Juazeiro do Norte, Ceara State, Brazil and a slag area in Lavrion District, Attica, Greece.^[4]