Description: Galena is a gray lead sulfide (PbS), the chief ore mineral of lead. One of the most widely distributed sulfide minerals, it occurs in many different types of igneous, sedimentary and metamorphic ore deposits; these include metalliferous veins, as at Broken Hill, Australia and Coeur d’Alene, Idaho; as replacements of limestone or dolomite (e.g., at Santa Eulalia, Mexico); and of contact-metamorphic origin (Darwin, CA). Ninety percent of all U.S. lead was found in "Mississippi River Valley deposits" which are concentrated in cavities and fracture zones of limestone and chert.
The number one use of lead today is in the lead-acid batteries that are used to start automobiles. The typical auto battery contains about twenty pounds of lead and must be replaced every four or five years. There are billions of these batteries in the United States alone.
Galena is very easy to identify. Freshly broken pieces exhibit perfect cleavage in three directions that intersect at 90 degrees. It has a distinct silver color and a bright metallic luster. Its density is most surprising; specimens always feel much heavier than one would expect based on size.
Health Warning: Galena specimens (lead) can be dangerous to your health, so always wash your hands after handling. Avoid inhaling dust when breaking. Do not lick or ingest. The CDC warns that exposure to high levels of lead may cause anemia, weakness, kidney and brain damage and eventually death. Pregnant women who are exposed to lead also expose their unborn child which can damage a developing baby’s nervous system.
Chemical Formula: PbS (lead sulfate)
Crystal Form: Commonly cubes, but also octahedrons, cube-octahedron combinations, and rarely dodecahedrons.
Crystal System: Isometric
Color: Lead-grey
Streak: Lead-grey
Luster: Metallic, Dull
Fracture: Sub-Conchoidal
Cleavage: Perfect, cubic, three directions at right angles
Hardness: Soft, 2.5 on Moh’s scale (about as hard as a fingernail - note all the scratches on the sample)
Density/Specific Gravity: 7.4-7.6 g/cm3 (this specimen feels heavy, even for a metallic mineral)
Magnetism: N/A
Taste: N/A
Hydrochloric acid: N/A
Radioactivity: N/A
Fluorescence: N/A
Distinguishing Physical Properties:
Specific gravity: dense, heft (samples of galena feel significantly heavier than similar-sized samples)
Color: Lead-grey color
Luster: dull metallic
Hardness: very soft, hardness of a fingernail
Cleavage: perfect in three directions (cubic)
Photograph Attribution: Galena specimen photograph by Sean C. Murphy, 2020.