Dictionary:

galena

  (gə-lē'nə)

A gray mineral, essentially PbS, the principal ore of lead.

[Latin galēna, lead ore.]

A mineral with composition PbS (lead sulfide) and belonging to the rock salt (NaCl) structure type. Galena usually occurs as cubes, sometimes modified by the octahedral form, with perfect cubic cleavage, brilliant metallic luster, color lead gray, specific gravity 7.5, and hardness 2½ on Mohs scale.

Galena is widely distributed and constitutes by far the most important ore for lead. Silver, antimony, arsenic, copper, and zinc minerals often occur in intimate association with galena; consequently, galena ores mined for lead also include many valuable by-products. Important localities include Broken Hill, Australia; the tristate district of Missouri, Kansas, and Oklahoma; and numerous occurrences in Colorado, Montana, and Idaho.

For more information on galena, visit Britannica.com.

Environment

In medium- to low-temperature ore veins, in igneous and sedimentary rocks, and disseminated through sediments.

Crystals are very common, usually cubic, sometimes octahedrons. They may also show combinations of several forms of the cubic system. Frequently in granular masses, often very fine-grained or fibrous.

Lead-gray. Luster metallic; hardness 2Ɖ-2Ɛ; specific gravity 7.4-7.6; fracture even (rarely seen); cleavage perfect cubic, with occasional octahedral parting. Brittle.

Lead sulfide (86.6% lead, 13.4% sulfur). Often contains silver, arsenic, antimony, and other impurities.

Fuses on charcoal, with yellow coating around the bead, and can be reduced to lead. Makes cloudy solution in nitric acid, with sulfur and lead sulfate separating out.

The ready cubic cleavage, with the lead gray metallic color and luster, is characteristic. Might be confused with dark sphalerite, in which case the light streak of the latter would permit a distinction. Other similar sulfides have good cleavages in a single direction, but not in three directions. The blowpipe reactions will help in very fine-grained (and deceptive) varieties.

The chief ore of lead, commonly found in shallow ore veins in which open cavities are frequent; hence, crystals are common and well developed. Unfortunately, their faces are usually dull. Commonly associated with the sulfides sphalerite, pyrite, and chalcopyrite, and with quartz, siderite, dolomite, fluorite, calcite, or barite as worthless associates (gangue minerals). The same mineral association occur in both sedimentary rocks and igneous rocks.

Fine distorted crystals have been found in Germany, and good examples in France, the former Yugoslavia, and elsewhere in Europe. The Joplin District of Missouri, Kansas, and Oklahoma is notable for its crystals, usually cubes, sometimes cubo-octahedrons with octahedral growths on the faces. Cen. Missouri is a recent source of relatively shiny cubic crystals, as is a mine in Madan, Bulgaria. Uncommon flattened and shiny spinel-twinned cubo-octahedral crystals seem to be characteristic of a good Mexican (Naica) occurrence. There are many occurrences of fine examples of this mineral.

Through near-surface alteration, particularly of the finer-grained examples, galena produces many other lead minerals such as anglesite, cerussite, and phosgenite. It often contains enough silver to make it an important source of that metal. It is commonly thought that galena with flaky curving cleavage planes--irregular rather than smooth, often slightly tarnished--is likely to be higher in the silver impurity.

A mineral containing lead.

Galena lanita
Galena crystal from Kansas
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's unit cell

Galena is the natural mineral form of lead sulfide. It is the most important lead ore mineral.

Galena is one of the most abundant and widely distributed sulfide minerals. It crystallizes in the cubic crystal system often showing octahedral forms. It is often associated with the minerals sphalerite, calcite and fluorite.

Lead ore deposits

Galena deposits often contain significant amounts of silver as included silver sulfide mineral phases or as limited solid solution within the galena structure. These argentiferous galenas have long been the most important ore of silver in mining. 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 alters to anglesite (lead sulfate) or cerussite (lead carbonate).

Galena from Poland

Galena deposits are found in Wales, 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 U. S. states: Missouri and Wisconsin.

Galena uses

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

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, which were a potential source of disease.^[1]

Galena is a semiconductor with a small bandgap of about 0.4 eV which found use in early wireless communication systems. For example, it was used as the crystal in crystal radio sets, in which it was used as a point-contact diode to detect the radio signals. The galena crystal was used with a safety pin or similar sharp wire, and was known as a "cat's whisker". Scientists that were linked to this application are Karl Ferdinand Braun and Sir Jagdish Bose. In modern wireless communication systems, galena detectors have been replaced by more reliable semiconductor devices, however, silicon point-contact microwave detectors still exist in the market.

See also

• List of minerals

References

• Klein, Cornelis and Cornelius S. Hurlbut, Jr. (1985) Manual of Mineralogy, Wiley, 2nd ed., pp. 274-276, ISBN 0-471-80580-7
• Webmineral data
• Mindat with location data
• Franklin and Sterling Hill mineral deposits
• Mineral Data Publishing - PDF

Notes

1. ^ Metropolitan Museum of Art. The Art of Medicine in Ancient Egypt. (New York: The Museum, 2005), p. 10, ISBN 1-58839-170-1

External links

• Case Studies in Environmental Medicine (CSEM): Lead Toxicity
• ToxFAQs™: Lead
• Mineral information institute entry for lead

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