Greenockite

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Greenockite
Greenockite-259580.jpg
Greenockite crystals from Tsumeb Mine, Namibia (Picture width 1 mm)
General
CategorySulfide mineral
Formula
(repeating unit)
CdS
Strunz classification2.CB.45
Crystal systemHexagonal
Crystal classDihexagonal pyramidal (6mm)
(same H-M symbol)
Space groupP63mc
Unit cella = 4.136
c = 6.713 [Å]; Z = 2
Structure
Jmol (3D)Interactive image
Identification
Formula mass144.48
ColorHoney yellow, citron yellow, orange yellow
Crystal habitColloform - forming from a gel or colloidal mass; encrustations - forms crust-like aggregates on matrix; radial - crystals radiate from a center without producing stellar forms (e.g. stibnite)
TwinningRare on {1122} forming trillings
CleavageDistinct on {1122}, imperfect on {0001}
FractureConchoidal
TenacityBrittle
Mohs scale hardness3.0-3.5
LusterAdamantine to resinous
StreakYellow orange to brick red
DiaphaneityNearly opaque to translucent
Specific gravity4.8 - 4.9
Optical propertiesUniaxial (-)
Refractive indexnω = 2.529 nε = 2.506
Birefringenceδ = 0.023
PleochroismWeak
Ultraviolet fluorescenceyellow-orange fluorescence under UV when rich in zinc[citation needed]
Other characteristicsToxic
References[1][2][3]

Greenockite is a rare cadmium bearing metal sulfide mineral consisting of cadmium sulfide (CdS) in crystalline form. Greenockite crystallizes in the hexagonal system. It occurs as massive encrustations and as hemimorphic six-sided pyramidal crystals which vary in color from a honey yellow through shades of red to brown. The Mohs hardness is 3 to 3.5 and the specific gravity is 4.8 to 4.9.

Greenockite belongs to the wurtzite group and is isostructural with it at high temperatures. It is also isostructural with sphalerite at low temperatures. It occurs with other sulfide minerals such as sphalerite and galena, and is the only ore mineral of cadmium, most cadmium is recovered as a byproduct of copper, zinc, and lead mining. It is also known from the lead-zinc districts of the central United States.

It was first recognized in 1840 in Bishopton, Scotland, during the cutting of a tunnel for the Glasgow, Paisley and Greenock Railway. The mineral was named after the land owner Lord Greenock (1783–1859).[2][4]

Use[edit]

Greenokite, also known as "cadmium ochre", was used as a yellow pigment prior to cadmium being recognized as a toxic element. The extracted cadmium has various industrial use, such as electrical nickel-cadmium (NiCd) rechargeable batteries, electroplating, high temp alloys, plating steel and other metals that corrode easily, and use in control rods for some nuclear reactors.

References[edit]

External links[edit]

Crystal structure of greenockite