Galena

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Galena
GalenaFromKansas.jpg
General
Category Sulfides
Chemical formula lead sulfide (PbS)
Identification
Color Lead gray, silvery
Crystal habit Cubes and octahedra, tabular and sometimes skeletal crystals
Crystal system Isometric hexoctahedral
Cleavage Cubic
Fracture Flat (when cubic) to even
Mohs Scale hardness 2.5 - 2.75
Luster Metallic
Refractive index Opaque
Pleochroism None
Streak Lead gray
Specific gravity 7.4 - 7.6
Fusibility 2

Galena is the natural mineral form of lead sulfide. It is one of the most abundant and widely distributed sulfide minerals. It is the most important lead ore mineral. It is also an important source of silver, which is often found in the mineral. It was once used as the semiconductor (or "crystal") in crystal radio sets.

Contents

Lead ore deposits

Galena is often associated with the minerals sphalerite, calcite, and fluorite.

Galena deposits often contain significant amounts (up to one percent) of silver as included silver sulfide mineral phases or as limited solid solution within the galena structure. In addition, zinc, cadmium, antimony, arsenic and bismuth also occur in variable amounts in lead ores. Selenium substitutes for sulfur in the structure constituting a solid solution series. The lead telluride mineral altaite has the same crystal structure as galena. Within the weathering or oxidation zone, galena changes to anglesite (lead sulfate) or cerussite (lead carbonate).

Galena from Poland.

Galena deposits are found in France, Romania, Austria, Belgium, Italy, Spain, Scotland, England, Australia, and Mexico. Noted deposits include those at Freiberg, Saxony; Cornwall, Derbyshire, and Cumberland, England; the Sullivan mine of British Columbia; and Broken Hill, Australia. Galena also occurs at Mount Hermon in Northern Israel. In the United States it occurs most notably in the Mississippi Valley type deposits of the Lead Belt in southeastern Missouri, and in similar environments in Illinois, Iowa and Wisconsin. Galena also was a major mineral of the zinc-lead mines of the tri-state district around Joplin in southwestern Missouri and the adjoining areas of Kansas and Oklahoma. Galena is also an important ore mineral in the silver mining regions of Colorado, Idaho, Utah and Montana. Of the latter, the Coeur d'Alene district of northern Idaho was most prominent.

Galena is the official state mineral of the states of Missouri and Wisconsin.

Characteristics

Galena has practically the same crystal structure as halite (sodium chloride, NaCl). It crystallizes in the cubic crystal system, often showing octahedral forms. In addition, it is a semiconductor with a small bandgap of 0.4 electron volts (eV).

Uses

Dark gray cubes of galena with fluorite (purple) and calcite (white) from Illinois, United States

One of the earliest uses of galena was as kohl, which in ancient Egypt was applied around the eyes to reduce the glare of the desert sun and to repel flies, a potential source of disease.[1]

Galena is now the principal ore of lead. Also, given the large quantities of the mineral that are processed, argentiferous (silver-containing) galenas have long been the most important ore of silver. In addition, in the early days of wireless, it was used as the semiconductor (or "crystal") in crystal radio sets. Combined with a safety pin or similar sharp wire known as a "cat's whisker," the galena crystal became part of a point-contact diode used to detect radio signals.

See also

Notes

  1. Metropolitan Museum of Art. The Art of Medicine in Ancient Egypt. (New York: The Museum, 2005), p. 10. ISBN 1588391701

References

  • Farndon, John. 2006. The Practical Encyclopedia of Rocks & Minerals: How to Find, Identify, Collect and Maintain the World's best Specimens, with over 1000 Photographs and Artworks. London: Lorenz Books. ISBN 0754815412
  • Klein, Cornelis, and Barbara Dutrow. 2007. Manual of Mineral Science, 23rd edition. New York: John Wiley. ISBN 9780471721574
  • Pellant, Chris. 2002. Rocks and Minerals. Smithsonian Handbooks. New York: Dorling Kindersley. ISBN 0789491060
  • Shaffer, Paul R., Herbert S. Zim, and Raymond Perlman. 2001. Rocks, Gems and Minerals, Revised edition. New York: St. Martin's Press. ISBN 1582381321
  • Mindat.org. 2007. Galena. Mindat.org. Retrieved April 10, 2007.

External links

All links retrieved November 23, 2013.

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