In addition to mineral crystals, the oxide coatings that form on many metal surfaces are semiconductors and can rectify, and crystal radios have been improvised using detectors made from rusty nails, corroded pennies, and many other common objects.
In addition to mineral crystals, the oxide coatings of many metal surfaces act as semiconductors (detectors) capable of rectification. Crystal radios have been improvised using detectors made from rusty nails, corroded pennies, and many other common objects.