Various iron ores are popularly called ironstones. Thus, there is brown ironstone or limonite, red ironstone or hematite and magnetic ironstone or magnetite. The latter is especially widespread in the Banat, hence the Hungarian name “Vaskő” (lit. ironstone), similarly to the Romanian (Ocna de Fier = iron mine) and German (Eisenstein = iron stone) names of the settlement. Magnetite (Fe₃O₄) is not only one of the most important and best quality ores of iron, but it is also a natural magnet. Biogenic magnetite crystals are found in a wide variety of migratory animals as magnetic receptors (e.g., in bees, salmon, and migratory birds), but they have also been discovered in the human brain.
In the picture: Magnetite, Ocna de Fier, Romania. Image width: 6 cm. Photo by László Tóth