Galena, also called lead glance, is the natural mineral form of lead sulfide.  This specimen is from Bulgaria.  Galena is safe to handle, but it's important to avoid inhaling any dust from the mineral as it does contain lead.  

Galena Mineral in Radio
In 1900, American inventor Greenleaf Whittier Pickard first used galena crystals in simple radio receivers. These so-called “crystal sets” consisted of a long wire antenna, a tuning circuit with two concentrically positioned wire coils, a carbon-particle earphone and a pea-sized crystal of galena.

The galena mineral crystal performed two functions: it first converted alternating current into direct current; then it detected and separated the audio-wave component from the carrier-wave component of a radio-wave-induced microcurrent. Crystal set operators simply moved a flexible, pointed copper wire called a “cat’s whisker” across the galena crystal to locate the site that maximized the point-contact rectifier effect and the loudness of the audible earphone signal.

Galena is the main ore of lead, used since ancient times, since lead can be smelted from galena in an ordinary wood fire.  Galena typically is found in hydrothermal veins in association with sphalerite, marcasite, chalcopyrite, cerussite, anglesite, dolomite, calcite, quartz, barite, and fluorite. It is also found in association with sphalerite in low-temperature lead-zinc deposits within limestone beds.  Minor amounts are found in contact metamorphic zones, in pegmatites, and disseminated in sedimentary rock.

In some deposits the galena contains up to 0.5% silver, a byproduct that far surpasses the main lead ore in revenue. In these deposits significant amounts of silver occur as included silver sulfide mineral phases or as limited silver in solid solution within the galena structure. These argentiferous galenas have long been an important ore of silver.  Silver-bearing galena is almost entirely of hydrothermal origin; galena in lead-zinc deposits contain little silver.