Missouri State Mineral
Galena is a lead sulfide that sometimes contains traces of silver, copper, antimony, or arsenic. When first exposed to air, galena is steel-gray metallic, sometimes also with a bluish tint. It then tarnishes and becomes somewhat dull, but soap and water will temporarily remove the tarnish. Galena is the primary ore of lead and contains mostly lead. It is also an ore of silver, as specimens in some areas contain up to 20 percent silver.
Galena’s hardness of 2.5 to 3 on the Mohs scale means it is quite soft. It breaks easily into small cubes, and well-formed crystals can shatter with only slight pressure. Because galena contains lead, those handling specimens of this mineral should take care not to inhale the dust and to wash their hands after touching it.
In the United States, the finest specimens of galena come from the area where Kansas, Oklahoma, and Missouri meet, known as the tri-state mining district. The Joplin area and the Sweetwater Mine along the Viburnum Trend district of Missouri are famous for producing excellent crystals of galena. It is also found in many other counties in the state. Galena is the primary source of lead, and Missouri is the country’s top producer of lead. Galena was named the state mineral of Missouri on July 21, 1967 and is also the official state mineral of Wisconsin.
The word "galena" is derived from a Greek word galene, which means "lead ore." The Latin word galena means "given to lead ore" or "waste from melted lead."
FORMATION AND OCCURRENCE
Galena is found in ore veins and in sedimentary rock. It normally forms cubes and octahedrons, and occasionally a combination of the two. It can also form as masses, grains, flaky plates, and interesting, unique shapes. Galena is associated with pyrite, chalcopyrite, calcite, sphalerite, fluorite, and other minerals.
The process of extracting lead from galena is simple and has been done since as early as 3000 BCE. Galena was used in ancient Egypt as kohl, which was applied under the eyes to protect against the sun’s rays, disease-carrying flies, and eye ailments.
Galena is a semiconductor and was used in early wireless communications devices. A popular hobby in the 1930s was to make radios at home out of galena crystals and copper wire. Today, galena is no longer used as a semiconductor, but is important for lead, which has many applications in the electronics, communications, and construction industries.
Galena’s well-formed cubes and distinctive cleavage make the mineral popular among amateur geologists and mineral collectors.
The largest specimen of galena may be a crystal found in Laxey, Isle of Man, United Kingdom, in 1923. It is a cube with each side measuring 9.8 inches (25 cm). Similar, if not larger, specimens have reportedly been found in Rescheid and Bleialf mines, Germany, and in the Viburnum Trend district in Missouri.
Chemical Formula: (PbS)
Crystal Structure: Isometric cF8, Space Group Fm-3m, No. 225
Hardness (Mohs): 2.5-2.75
Color: Lead gray, silvery
Luster: Metallic, dull
Density: 7.58 g/cm3
Some data courtesy of the Mineralogical Society of America
Author: World Trade Press