Greenockite

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Greenockite
Greenockite-259580.jpg
Greenockite crystals from Tsumeb Mine, Namibia (Picture width 1 mm)
General
Category Sulfide mineral
Formula
(repeating unit)
CdS
Strunz classification 02.CB.45
Crystal symmetry Hexagonal dihexagonal pyramidal
H-M symbol: (6mm)
Space group: P 63mc
Unit cell a = 4.136 Å, c = 6.713 Å; Z=2
Identification
Formula mass 144.48
Color Honey yellow, citron yellow, orange yellow
Crystal habit Colloform - 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)
Crystal system Hexagonal
Twinning Rare on {1122} forming trillings
Cleavage Distinct on {1122}, imperfect on {0001}
Fracture Conchoidal
Tenacity Brittle
Mohs scale hardness 3.0-3.5
Luster Adamantine to resinous
Streak Yellow orange to brick red
Diaphaneity Nearly opaque to translucent
Specific gravity 4.8 - 4.9
Optical properties Uniaxial (-)
Refractive index nω = 2.529 nε = 2.506
Birefringence δ = 0.023
Pleochroism Weak
Ultraviolet fluorescence yellow-orange fluorescence under UV when rich in zinc[citation needed]
Other characteristics Toxic
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, and high temp alloys.

References[edit]

Crystal structure of greenockite