A solid rock stores electrical impulses for later play back. Magnetic tape can record and store for many years, sound and even video images as well as data. Devices are made with oxide metals; iron oxide was the first for cassette tapes, then chromium oxide. A magnetic field applied to the surface of the oxide metal coating, re-arranging the molecular structure into a pattern matching the source magnetic field. A magnet that mirrors the original energy, like a photograph does with physical objects. All is needed is a receiver that is capable of “reading” or “receiving” what has been recorded. A thin film of oxide metal and not a solid rock though. Metals are also crystals and have a crystalline structure. If a bar of iron (or a bar containing iron) is struck sharply upon concrete while facing north, the crystalline structure is shifted to match the Earth’s magnetic field, becoming a magnet itself. The impact is the sudden pressure forced upon the crystalline structure.