Covellite and Greenockite Composition, Crystallization and Structure

Covellite
Cupric sulphide, CuS. Hexagonal. Rarely in tabular hexagonal crystals with priminent basal plane. Usually massive. Perfect basal cleavage. H. = 1.5-2. G. = 4.59. Metallic luster. Color indigo-blue. Fusible at 2.5. Gives odor of sulfur dioxide in O.T. and much sulfur in C.T. The roasted mineral, moistened with hydrochloric acid and ignited, gives a blue flame (copper). When moistured with water shows a strong purple color. A rare mineral, found only in the enriched sulphide zone of copper deposits, associated with chalcocite, bornite, chalcopyrite, tetrahedrite, etc., and in most cases, if not always, is secondary in this origin.

Greenockite
Composition. Cadmium sulphide, CdS = Sulfur 22.3, cadmium 77.7.

Crystallization. Hexagonal; hemimorphic. Crystals hemimorphic, showing prism faces and terminated usually below with base and above with pyramids.}

Structure. Usually pulverulent, as thin powdery incrustations. Crystals small and rare.

Physical Properties. H. = 3-3.5. G. = 4-9.5. Luster adamantine to resinous, earthly. Color yellow.

Test. infusible. Yields odor of sulfur dixoded when heated B.B. or in O.T. Decomposed by hydrochloric acid with the evolution of hydrogen sulphide gas, which may be detected by its disagreeable odor. Gives a reddish brown coating of cadmium oxide when heated with sodium carbonate on charcoal. Characterized by its yellow color and pulverulent form.

Occurrence. Moss common mineral containing cadmium but found only in a few localities and is small amount. Associated usually with zinc ores, often as a coating on sphalerite and smith sonite. Found in crystals at Bishopton, renfrewshire, Scotland; with the zinc ores of southwestern Missouri and in Arkansas, also in Bohemia and California and Carinthia.

Use. A source of cadmium. Cadmium-beaing zinc ores furnish the greater part of metal produced. Cadmium is used in alloys for dental and other purposes. The sulphide serves as a yellow pigment.