7.2-7.6 Galena is a widely distributed and very common mineral which is the most important ore of the elemental metal lead. It is commonly associated with zinc and copper sulfides and silver minerals, and is not uncommonly silver bearing. Galena is a typical hydrothermal mineral of medium temperature deposits which is also found in sedimentary and metamorphic deposits. In hydrothermal veins it is commonly associated with bournonite, chalcopyrite, pyrite, sphalerite and tetrahedrite and with the gangue minerals barite, calcite, dolomite, fluorite and quartz. In replacement deposits and high temperature veins, galena is associated with minerals such as biotite, diopside, feldspar, garnet, and rhodonite.
Galena commonly occurs as granular masses with many shiny surfaces.
It also occurs with cubic, cubo-octahedral and octahedral crystals. Galena crystals are opaque with a rich metallic luster. It blackens with time as a result of oxidation. This particular specimen is from the Westfork Mine in Reynolds County, Missouri, which is located in the center of the southeast quadrant of the state. That's a roll of 35mm film included in the picture to establish the scale of this specimen.