Greenockite is a rare cadmium

Cadmium

Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Similar to zinc, it prefers oxidation state +2 in most of its compounds and similar to mercury it shows a low...

 mineral

Mineral

A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...

 that consists of cadmium sulfide

Cadmium sulfide

Cadmium sulfide is the inorganic compound with the formula CdS. Cadmium sulfide is a yellow solid. It occurs in nature with two different crystal structures as the rare minerals greenockite and hawleyite, but is more prevalent as an impurity substituent in the similarly structured zinc ores...

, CdS, in crystalline form. Greenockite crystallizes in the hexagonal

Hexagonal crystal system

In crystallography, the hexagonal crystal system is one of the 7 crystal systems, the hexagonal lattice system is one of the 7 lattice systems, and the hexagonal crystal family is one of the 6 crystal families...

 system. It occurs as massive encrustations and as 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

Specific gravity

Specific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...

 is 4.5 to 5.

Greenockite occurs with other sulfide minerals such as sphalerite

Sphalerite

Sphalerite is a mineral that is the chief ore of zinc. It consists largely of zinc sulfide in crystalline form but almost always contains variable iron. When iron content is high it is an opaque black variety, marmatite. It is usually found in association with galena, pyrite, and other sulfides...

 and galena

Galena

Galena is the natural mineral form of lead sulfide. It is the most important lead ore mineral.Galena is one of the most abundant and widely distributed sulfide minerals. It crystallizes in the cubic crystal system often showing octahedral forms...

. It is the only ore mineral of cadmium, most cadmium is recovered as a byproduct of zinc and lead mining.

It was first recognized in 1840 in Bishopton

Bishopton, Renfrewshire

Bishopton is a large village in Renfrewshire, Scotland, a few miles west of Erskine.-Transport links:Bishopton sits a couple of miles from the southern end of the Erskine Bridge, which spans the River Clyde between Renfrewshire and West Dunbartonshire. Part way along the B815 road is a computer...

, Scotland

Scotland

Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...

, during the cutting of a tunnel for the Glasgow, Paisley and Greenock Railway

Glasgow, Paisley and Greenock Railway

The Glasgow, Paisley and Greenock Railway was an early railway, which merged with the Caledonian Railway. It was created to provide train services between Greenock and Glasgow.-History:...

. The mineral was named after the land owner Lord Greenock

Charles Cathcart, 2nd Earl Cathcart

Charles Murray Cathcart, 2nd Earl Cathcart GCB was a British Army general who became Governor General of the Province of Canada and Lieutenant Governor of Canada West .-Life:Cathcart, eldest surviving son of William Schaw Cathcart, 1st Earl Cathcart, was born at...

. It is also known from the lead-zinc districts of the central United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

.