Galena is a lead sulfide mineral (PbS). It has a metallic luster, silvery-gray color, cubic crystals, cubic cleavage, is moderately soft, and has a very high specific gravity (it's very heavy for its size).
Galena is the most important lead ore mineral. It's principally found in hydrothermal vein systems and in Mississippi Valley-type deposits. Silver (Ag) can fall into the lead position as an impurity, sometimes in relatively high proportions. This results in argentiferous galena, (Pb,Ag)S.
Historically, lead from galena has been used as a gasoline additive, a paint ingredient, and for making bullets. Lead is also used to make various metal products, batteries, radiation shielding, etc.
Galena from the Tri-State District (West Fork Mine, Reynolds County, Missouri, USA) (CMC RM 1142, Cincinnati Museum Center's rock & mineral collection, Cincinnati, Ohio, USA).