Greenockite - Encyclopedia

GREENOCKITE

    Class : Sulfides and sulfosalts
    Subclass : Sulfides
    Crystal system : Hexagonal
    Chemistry : CdS
    Rarity : Quite common

Greenockite is a relatively common hydrothermal mineral found in zinc-rich, cadmium-bearing hydrothermal veins, as well as in cavities in some basic rocks. It is the most common cadmium mineral. It was named in honor of Charles Murray Cathcart, Lord Greenock, a British Army officer who discovered the mineral. Greenockite generally occurs as lemon-yellow powdery coatings or earthy crusts on sphalerite ; it has an adamantine to resinous luster. The crystals are very rare, hemimorphic pyramidal with conical or tabular endings, they barely exceed 1 cm. It is anecdotally a cadmium ore.

Main photo : Greenockite on calcite from Joplin, Missouri, USA - Smithsonian Institute Collection © Ken Larsen

Greenockite from Prospect Park, Passaic County, New Jersey, USA © Jason B. Smith
Greenockite from Siglo Veinte Mine, Llallagua, Potosí, Bolivia © Vincent Bourgoin
Greenockite from Bishopton, Renfrewshire, Scotland, UK © Herwig Pelckman
Greenockite from Echassières, Allier, France © Michael Förch

Greenockite in the World

The most beautiful greenockite crystals come from the type locality : Bishopton (Scotland) ; they do not exceed 12 mm and are implanted on prehnite. Significant zinc deposits have yielded millimetric red-orange crystals, notably Llallagua, Pulacayo and Asunta (Bolivia), but the most spectacular specimens are lemon yellow coatings on calcite scalenohedra (Joplin, Missouri) or on smithsonite (Masua , Sardinia, Italy).

Greenockite in France

In France, greenockite coatings have been described in Pierrefitte (Pyrénées), and in Plélauff (Côtes d'Armor). It is also reported at Echassières (Allier), at Lachaux (Puy-de-Dôme), at St-Laurent-le-Minier and St-Bresson (Gard), at Nontron (Dordogne), at Peyrebrune (Tarn), at the Tistoulet mine (Aude), in Orpierre (Hautes-Alpes), as well as in many other locations.

Twinning

There is a known and rare twinning plane on {11-22}.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 3 to 3.5
Density : 4.8 to 4.9
Fracture : Conchoidal
Streak : Yellow

TP : Translucent to transparent
RI : 2.506 to 2.529
Birefringence : 0.023
Optical character : Uniaxial -
Pleochroism : Low
Fluorescence : Yellow

Solubility : Hydrochloric acid

Magnetism : NoneRadioactivity : None