Apachite

Apachite
General
Category	Silicate mineral
Formula (repeating unit)	Cu9Si10O29·11(H2O)
IMA symbol	Apa
Strunz classification	9.HE.10
Crystal system	Monoclinic Unknown space group
Unit cell	a = 12.89, b = 6.055 c = 19.11 [Å], β = 90.42° V = 1,490.24 Å3; Z = 2
Identification
Formula mass	1514.92 g/mol
Color	light blue
Crystal habit	spherical, rounded aggregates
Mohs scale hardness	2
Luster	nonmetallic, silky
Streak	light blue
Diaphaneity	translucent
Specific gravity	3.37
Optical properties	biaxial negative
Refractive index	nα=1.610, nβ=1.650, nγ=1.650
Birefringence	δ = 0.040
2V angle	Small
References

Apachite is a copper silicate mineral with a general formula of Cu₉Si₁₀O₂₉·11H₂O. The name is associated with the Apache tribe residents of the area near the Christmas copper mine in the Dripping Spring Mountains of Gila County, Arizona, the location where apachite was first described in 1980.

Apachite has monoclinic crystal symmetry, displaying 3 axes of unequal length with two of the axes perpendicular to each other as well as one angle oriented less than 90°. The mineral has a maximum birefringence value of δ = 0.040 which describes the difference between the highest and lowest index of refraction for the mineral. Apachite is an anisotropic mineral, so the velocity of light varies for this mineral.

It occurs in retrograde metamorphic environment as fractures cutting garnet diopside skarn. It occurs associated with kinoite, gilalite, stringhamite, junitoite, clinohedrite, xonotlite, apophyllite, calcite and tobermorite.