Zunyite

Zunyite
Sharp, pyramids of brown-red zunyite from Silver City, Tintic District, East Tintic Mountains, Juab County, Utah, US (size: 5.5 x 5 x 3.5 cm)
General
Category	Sorosilicates
Formula (repeating unit)	Al13Si5O20(OH,F)18Cl
Strunz classification	9.BJ.55
Crystal system	Isometric
Crystal class	Hextetrahedral (43m) H-M symbol: (43m)
Space group	F43m
Unit cell	a = 13.8654 - 13.8882 Å; Z = 4
Identification
Color	Grayish white, flesh-red; colorless in thin section
Crystal habit	Crystalline - occurs as well-formed fine sized crystals
Twinning	On {111}, contact and penetration
Cleavage	Good on {111}
Fracture	Uneven
Tenacity	Brittle
Mohs scale hardness	7
Luster	Vitreous
Streak	White
Diaphaneity	Transparent to translucent with inclusions
Specific gravity	2.874(5) (meas.) 2.87 - 2.90 (calc.)
Optical properties	Isotropic
Refractive index	n = 1.592 - 1.600
Other characteristics	May fluoresce red under UV
References

Zunyite is a sorosilicate mineral, Al₁₃Si₅O₂₀(OH,F)₁₈Cl, composed of aluminium, silicon, hydrogen, chlorine, oxygen, and fluorine.

Zunyite occurs in highly aluminous shales and hydrothermally altered volcanic rocks. It occurs in association with pyrophyllite, kaolinite, alunite, diaspore, rutile, pyrite, hematite and quartz.

It was discovered in 1884, and named for its discovery site, the Zuni mine in the Silverton District, San Juan County, Colorado.