Galena, sulphuret of lead, the ore which furnishes most of the lead of commerce. It occurs in highly crystalline masses, which separate into cubical fragments. Its structure is also granular, and sometimes fibrous. Freshly fractured, it presents a brilliant lustre like polished steel, which changes by exposure to a dull lead-gray color. Its hardness is from 2.5 to 2.75; specific gravity, 7.25 to 7.7. Its composition, represented by the symbol PbS, is lead 86.6, sulphur 13.4; but it often contains other metals, as antimony, silver, zinc, iron, and copper, as well as the substance selenium. It is also largely intermixed with the earthy gan-gues that form the principal portion of the veins in which it is found. From these, and from the sulphurets of zinc and the pyritous copper and iron usually associated with the ore, it is separated as far as practicable before smelting by the processes of stamping or crushing, jigging, etc. (See Lead, and Metallurgy.) In some veins and beds it is frequently found in large groups of cubical crystals, which are very free from foreign substances. In this form it is met with in the fissures in the limestone of the lead region of Wisconsin, Iowa, and Illinois, imbedded in the clay with which the fissures are filled.
Galena is a valuable ore for the silver it often contains, as well as for the lead. In reducing the ore by smelting, the silver all goes with the lead, which is run out; and from this it is separated either by the process of cupellation, or parting by crystallization, or other method. The lead ores however do not all contain silver enough to render its extraction profitable, although the separation is so cheaply conducted that 3 oz of silver to the ton of lead will pay for the operation. Galena rich in silver is a product of numerous veins in the granitic and meta-morphic rocks of New England and the Pacific states; but the more argentiferous it is, the less certain is the yield of the veins in quantity, and few of this character have been found profitable to work. In Cornwall and Devonshire, England, mines of argentiferous galena have been worked profitably for centuries, even when a product of 9 or 10 oz. of silver to the ton of silver-lead was required to pay the expense of separation. The richest metal was from the ores of mines near Beer Alston in Devonshire, which yielded from 80 to 120 oz. of silver to the ton of lead; one portion of the mines, known as the South Hooe, yielded lead containing 140 oz. of silver to the ton.
These mines, though now of little importance, were famous for their production in the time of Edward I. and II. The most celebrated mines of argentiferous galena in the United States are those of the Washoe district, Nevada. Galena may be formed artificially by fusing lead with sulphur.