Galena

Mineral Name: Galena

Chemical Composition: PbS.

Color: The mineral, if fresh, is bright silver in color with a metallic luster and dulls into a lead grey color as it tarnishes (1).

Streak: Lead grey to black

Hardness: 2.5-3

Cleavage/Fracture: Cleavage is perfect, cubic with three directions at right angles.

Crystal Form: Crystals may occur as cubes, octahedrons, or a combination of the two forms.

Luster: Metallic

Special Features: One of the most notable features of Galena is that it melts at a relatively low temperature compared to other metals. Archeologists have found lead beads and statues that date back to about 6500 BC, with the lead in these materials presumably being processed from the mineral galena (1). It was not until 2000 years ago that the Greeks and Romans were able to separate silver from lead (1).

Varieties: Galena has two varieties, Acerila and Argentiferous galena. Acerila is a term used in certain South American countries to describe granular Galena (2). Argentiferous galena is galena with a much larger silver content as opposed to the average silver content of one percent (2). Because of the silver content in Argentiferous galena, the crystal structure may have a curved cleavage face, which is not seen in the less silver-rich versions of galena (1). Galena may also contain impurities such as silver, arsenic, antimony, and copper.

Mineral Group: Galena belongs to the sulfide group. Sulfide minerals contain the sulfide anion (S2-) and are important metal ores. (1).

Environment: Galena can form in hydrothermal metamorphic environments such as hypothermal/mesothermal veins that are exposed to extremely hot liquids at extreme or semi-extreme depths as well as in hydrothermal replacement deposits. Galena can also be found in sedimentary placer deposits, which is the settling of matter after being carried downstream by a water current. Lastly, and strangely enough, on the planet of Venus the mountains are covered with snow, but not like the snow found on Earth. Venus is too hot and the mountains are instead capped with a metallic frost of galena and bismuthinite. (6)

Associated Rock types: Galena is usually found in sedimentary limestone and dolostone deposits and even some breccias (1). It can also, though rarely, be found in basalts and diabase (2).

Occurrence in North America: In the United States, Galena can be found primarily in the Mississippi Valley. Mining for this material was also common in Missouri, Illinois, Iowa, Wisconsin, Kansas, and Oklahoma. Galena could also be found in the silver mining regions of Colorado, Idaho, Utah, and Montana (3).

Economic Uses: In the medical field, lead (found in galena) is primarily used to block out harmful radiation waves while performing X-rays on patients as well as the staff themselves (4). Because of the high density in lead when the radiation rays hit it it absorbs the ray and/ or deflects the rays.

Industrial Uses: One of the most notable uses of galena is that it is an ore that is used for most of the world’s lead production. This lead is then used for lead-acid batteries found in cars. Lead-acid batteries were the first rechargeable batteries in commercial use. These batteries were used for automotives such as cars, golf carts, and forklifts (7). The average car battery lasts about five years (5).

First Notable Identification: Galena was first named by Pliny the Elder, and galena means lead ore in Greek (1).

How We Identified It: The way we saw Galena is that it is much more cubic in shape when you compare it to other, similar minerals. It is metallic and it is much heavier than any other material that we handled with a similar size due to its high density. This material contains lead; thus, we must know that it should be carefully handled (don’t lick it).

Don’t Confuse It With: There are quite a few minerals that are similar to Galena. Sphalerite is missing the cubic cleavage, it is lighter in weight, and has a white or light brown streak. Stibnite lacks the cleavage and has a different crystal form (2). Acanthite is much softer and is sectile, meaning it can be cut smoothly (2). Jamesonite lacks similar cleavage, it is slightly lighter in weight, and it has a different crystal form. Chalcocite has a different crystal form, it is much darker, and it is lighter in weight (2). And lastly, Tetrahedrite is harder, has a darker color, and is much lighter in weight. The main difference between all these minerals and Galena is that they are different in weight and lack Galena’s cleavage (2).