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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