· Magnetite. Limonite. Siderite. The iron minerals that are at present used as ores are hematite, magnetite, limonite, and siderite; also, occasionally ankerite, goethite, and turgite. Hematite is the most important iron ore. The iron content of the pure minerals is as follows: Ankerite is a carbonate of lime, magnesia, manganese, and iron.