Cubic Galena Crystal with Marcasite
Lead Sulfide, PbS
Crystal System: Cubic
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.
The largest lead and zinc deposits in the United States are located in the Tri-State mining district (Missouri, Kansas, Oklahoma) near Joplin, Missouri. 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. The crystal has a longest edge of four and a half inches and tips the scales at eighteen and a half pounds. As I said, it's "heavy lead"! ;)
Iron Sulfide, FeS2
Crystal System: Orthorhombic
Marcasite is a common mineral which occurs in low temperature hydrothermal veins, often in association with lead and zinc sulfides. It also occurs in sedimentary deposits as a precipitate created by the action of acid waters in reduction zones. Marcasite is dimorphic with Pyrite.
Marcasite occurs as flattened prismatic crystals which are often twinned. It commonly occurs as concretionary, massive, nodular, or radiate aggregates with an opaque, greenish tinged yellow color and a metallic luster.
Large amounts of marcasite are found in the United Sates in the Tri-State mining district and Galena, Illinois. Marcasite has industrial uses in the production of sulfuric acid.
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