GALENA, lead sulfide, is the principal ore of lead. It is steel gray,
heavy, opaque, and has a bright metallic luster, though the shiny
surface may be dulled by a coating of lead carbonate. It has a gray or
black streak, is soft enough to mark paper, and can be scratched by a
penny. The cube-shaped crystals readily break into cubic, right-angled
fragments. Probably the most obvious features of the mineral are its
bright metallic luster on fresh surfaces, high specific gravity, and
cubic cleavage.
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At many places galena is argentiferous (silver-bearing), but Illinois
galena is relatively unimportant for its silver content. As a source of
lead, however, it is an important commercial product of the state.
Scattered pieces of galena are found at many places in Illinois. Some
occur in the glacial deposits, others occur as small pockets and as
crystals in limestones and geodes. In only two areas of the state are
deposits of commercial value. In northwestern Illinois galena occurs in
association with sphalerite; in extreme southern Illinois it occurs in
association with fluorite and sphalerite.