Galena, Chalcopyrite, Sphalerite & Calcite

Galena was the heart of the first crystal radios. Acting as a natural semiconductor, it let a fine wire called the cat's whisker pull voices from the air with no battery at all.

Brassy and gold-flecked, chalcopyrite is the single most important source of copper on Earth, the ore behind most of the metal in modern wiring.

Sphalerite is named from the Greek for treacherous, because it fooled old miners hunting for lead. Gem-clear pieces hide a second surprise: they scatter light into rainbow fire more than three times stronger than a diamond.

Look through a clear rhomb of Iceland spar calcite and the world doubles, split into twin images by the crystal's double refraction. Some researchers think Norse sailors used this very effect to find the sun through cloud, the so-called sunstone, though the idea remains a debated hypothesis.