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Galena

earth science Maturity 9-11 Next article →

Galena, also known as lead glance, is a naturally occurring mineral. It is the primary ore of lead, which is a metal used in many ways. It is also a significant source of silver. Galena is one of the most widely distributed sulfide minerals on Earth.

Galena Sweetwater Minéraux SU
Galena Sweetwater Minéraux SU

This means it is made of sulfur and a metal. It is an essential material for both modern industry and ancient history.

At a microscopic level, galena has a very organized structure. It belongs to the octahedral sulfide group of minerals. In this group, metal ions sit in specific positions called octahedral positions. Galena is made of divalent lead cations and sulfur anions. These atoms form a close-packed cubic unit cell. This internal arrangement is very similar to the structure of halite, which is common table salt.

Baryte-Galena-Pyrite-203072
Baryte-Galena-Pyrite-203072

Because of this structure, galena often grows in a cubic crystal system. It can also form octahedrons, which are shapes with eight sides.

Galena is often found alongside other specific minerals. It frequently occurs in hydrothermal veins. These are cracks in the Earth's crust filled by hot, mineral-rich water. In these veins, you might find it with sphalerite, calcite, or fluorite. It also appears with marcasite, chalcopyrite, and quartz. Sometimes, it is found in low-temperature lead-zinc deposits within limestone beds. It can even be found in contact metamorphic zones or scattered in sedimentary rock.

History shows that humans have used galena for thousands of years. In Ancient Egypt, it was used to make kohl, an eye cosmetic. This helped reduce the glare of the desert sun and repelled flies. In pre-Columbian North America, indigenous peoples used it for decorative paints and cosmetics. They traded the mineral across the eastern United States.

Galena Sweetwater Minéraux SU
Galena Sweetwater Minéraux SU

In the 19th century, galena played a role in early technology. It is a semiconductor, which means it can control the flow of electricity. Early radio users used a galena crystal and a sharp wire called a "cat's whisker" to detect radio signals.

CatWhisker
CatWhisker

Many famous deposits of galena exist around the globe. In the United States, the largest known deposit is the Lead Belt in southeastern Missouri. It is also found in the Driftless Area of Illinois, Iowa, and Wisconsin. This area is so important that the state of Illinois, Iowa, and Wisconsin all have galena in their names. In Australia, many deposits formed about 1,680 million years ago. Australia was the world's leading producer of lead in 2021.

Baryte-Galena-Pyrite-203072
Baryte-Galena-Pyrite-203072

Other notable locations include Cornwall in England and the Linares mines in Spain.

Silver is a very important byproduct of galena mining. In some deposits, galena contains up to 0.5% silver. This silver can actually bring in more revenue than the lead itself. This silver usually exists as silver sulfide minerals inside the galena. Most silver-bearing galena comes from hydrothermal origins. In other types of lead-zinc deposits, there is much less silver present. This makes the silver-rich deposits very valuable to miners.

While galena is useful, it must be handled with care. As a pure specimen, it is insoluble in water and almost non-toxic to hold. However, lead(II) sulfide can be highly toxic if it is inhaled or swallowed. This is especially true with repeated or long-term exposure. In the environment, galena can change through weathering. It can turn into anglesite, which is lead sulfate, or cerussite, which is lead carbonate. Even tiny bacteria and archaea can help turn galena into anglesite through a process called oxidation.

Baryte-Galena-Pyrite-203072
Baryte-Galena-Pyrite-203072
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