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
IMA symbol	Sha[1]
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	[2][3][4]

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.[5]