Galena

Galenite ; lead glance ; blue lead ; potter's ore ; dice ore ; steel ore. Name derived from the Greek galena (tranquility) because of its supposed soothing effect in certain ailments. Alquifoux (Fr.) ; Archifoglio (It.) ; Bleiglanz (Germ.)

Lead sulphide. PbS; Ph = 86.60 per cent. S = 13.40 per cent., total 100. Usually contains silver sulphide. Common impurities include zinc, copper, iron, cadmium, etc.

Isometric; hexoctahedral. Common form, cubic or cubo-octahedral. sometimes tabular. Also in massive or in coarse or fine granular forms. Twinning not very common but twin plane {111} occurs in penetration and contact twins. Twin plane {114}, lamellar. Twin plane {144} caused by deformation.

S.G. 7.58 ± 0.01. H. = 2½-2¾; nearly sectile. Lustre, bright, metallic often tarnished to dull. Colour, lead-grey. Streak, black to lead-grey. Cleavage, perfect, cubic {100} : Fracture, flat, subconchoidal; Optical properties, opaque, in polished section, isotropic; Fusibility, 2; M.P., 1115° C.

Galena oxidises to lead sulphide (anglesite) and to lead carbonate (cerussite).

Galena is readily recognised by its cubic habit, good cleavage, high specific gravity, low hardness and its black streak.

In the open tube, gives off sulphurous fumes. In the reducing flame on charcoal, galena is reduced to metallic lead together with a yellow to white coating of lead oxide. In the oxidising flame, gives a heavier coating of white volatile oxides of lead and sulphur. Sulphur dioxide odour given off on heating on charcoal. Decomposed by nitric acid with the separation of sulphur and the formation of white lead sulphate. Decomposed by hydrochloric acid with evolution of H₂S, the solution thus produced when cooled gives white crystals of lead chloride soluble on heating.

Galena is the commonest and most important of the lead minerals and is one of the commonest and widespread of all the sulphide minerals. Often associated with sphalerite, pyrite, marcasite, chalcopyrite, etc.

Chiefly as hydrothermal lodes or veins in sedimentary rocks, as metasomatic replacements and disseminations in limestones and dolomites and as residual deposits. Pyrometasomatic and contact-metamorphic and sedimentary deposits of galena are of minor importance.

World production of lead in recent years has been about 1¾ million tons a year. The major producing areas include the Coeur d’Alene district of Idaho, the Tri-State area (Missouri-Oklahama-Kansas) of the U.S.A., and the Broken Hill deposits in New South Wales. The Sullivan mine in British Columbia is the largest single lead-zinc mine in the world. Mexico and the U.S.S.R. are also very large producers of lead.