Shattuckite

Shattuckite is a copper silicate hydroxide mineral with formula Cu₅(SiO₃)₄(OH)₂. It crystallizes in the orthorhombic – dipyramidal crystal system and usually occurs in a granular massive form and also as fibrous acicular crystals. It is closely allied to plancheite in structure and appearance.

Shattuckite
General
Category	Inosilicate
Formula (repeating unit)	Cu5(SiO3)4(OH)2
Strunz classification	9.DB.40
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Pcab
Identification
Color	Dark and light blue, turquoise
Crystal habit	Commonly spherulitic aggregates of acicular crystals
Cleavage	perfect along [010] and [100]
Fracture	uneven
Mohs scale hardness	3.5
Luster	Dull to silky
Streak	Blue
Diaphaneity	Translucent to opaque
Specific gravity	4.1 (rather heavy for a non-metallic mineral)
Optical properties	Biaxial (+)
Refractive index	nα = 1.753, nβ = 1.782, nγ = 1.815
Pleochroism	X = very pale blue; Y = pale blue; Z = deep blue
References	[1][2][3]

Shattuckite is a relatively rare copper silicate mineral. It was first discovered in 1915 in the copper mines of Bisbee, Arizona, specifically the Shattuck Mine (hence the name). It is a secondary mineral that forms from the alteration of other secondary minerals. At the Shattuck Mine, it forms pseudomorphs after malachite. A pseudomorph is an atom by atom replacement of a crystal structure by another crystal structure, but with little alteration of the outward shape of the original crystal. It is sometimes used as a gemstone.[4]