Quick answer: Galena is lead sulfide (PbS), the world’s main ore of lead and often an important source of silver. It forms bright silver-gray cubes because its atoms sit in the same simple cubic pattern as table salt, and it breaks into smaller cubes along three cleavage planes. It is very heavy, with a specific gravity of about 7.5. Wash your hands after handling it.
Galena is one of the few common minerals whose crystal habit gives away its internal structure almost without a magnifying glass: it grows as sharp, well-formed cubes, sometimes with the corners slightly trimmed into an octahedral face, a shape direct enough that it’s one of the standard teaching examples for the cubic crystal system.
Lead sulfide, and lead’s main ore
Galena is lead sulfide, PbS, and it has been humanity’s primary source of lead for thousands of years, mined and smelted since antiquity for uses ranging from Roman plumbing to modern batteries. It typically forms in hydrothermal veins alongside sphalerite, another sulfide mineral, and often carries trace silver as an economically important byproduct, which historically made galena deposits worth mining for two metals at once.
Why the cubes form so cleanly
Galena’s cubic habit comes directly from how lead and sulfur ions pack together, alternating in a simple, highly symmetric repeating grid, the same basic atomic logic behind why the cubic system produces such geometrically clean crystals across very different minerals, from galena’s metallic cubes to pyrite’s brassy ones to halite’s salt cubes. That same structure gives galena perfect cubic cleavage, breaking cleanly along three directions at right angles, which is part of why intact, sharp-edged galena crystals are prized separately from the ordinary massive ore ground up for processing.
Galena is also notably dense, one of the heavier common minerals by volume, dense enough that experienced collectors can often identify it by weight alone before checking anything else, a property covered in more depth in our piece on specific gravity.
Galena at a glance
- Chemistry: lead sulfide, PbS
- Hardness: 2.5 on the Mohs scale
- Density: about 7.4 to 7.6 g/cm³, so a piece feels roughly three times heavier than quartz of the same size
- Streak: lead-gray
- Cleavage: perfect in three directions at right angles, so it breaks into smaller cubes
Common questions about galena
Why does galena form cubes?
Galena has the same atomic arrangement as table salt: lead and sulfur atoms alternate in a simple cubic grid. Crystals tend to show the faces that match their internal structure, so galena grows as cubes, and even breaks into cubes when struck. Our post on cleavage vs. fracture explains why some minerals break this cleanly.
Is galena safe to touch?
Galena contains lead, so treat it with sensible care. Handling a specimen is generally considered low risk, but wash your hands afterward, keep it away from small children and pets, never lick it or put it in drinking water, and do not sand, cut, or grind it, since the dust is the real hazard.
Why is galena so important historically?
It has been the world’s main source of lead for thousands of years, and often of silver too, because silver commonly substitutes into galena deposits. In the early days of radio, galena crystals were also used as detectors in “crystal radio” sets: a thin wire called a cat’s whisker touched the crystal to pick up a signal.
Where is galena found?
Galena is common in hydrothermal veins and in lead-zinc deposits hosted in limestone, often alongside sphalerite, calcite, and fluorite. It occurs across the northeastern U.S., including in New York and New Jersey mineral localities.
