By mass it is the most common element on the Earth.
Iron ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, deep purple, to rusty red. The iron itself is usually found in the form of
magnetite – Fe3O4 – 72.4% Fe
hematite- Fe2O3 – 69.9% Fe
goethite – FeO(OH) – 62.9% Fe
limonite – (FeO(OH).n(H2O))
siderite – FeCO3 – 48.2% Fe
Ores carrying more than 60% Fe are known as “natural ores” or “direct shipping ores”, meaning they can be fed directly into the blast furnaces. This iron ore used to make pig iron from which steel is made.
Mineral of the Month: February 2015
Magnetite– Fe3O4 – (māg’nĭ-tīt’)- Iron ore that is naturally magnetic. Magnetite is the most magnetic of all the naturally occurring minerals on Earth. Naturally magnetized pieces of magnetite, called lodestone, will attract small pieces of iron, and this was how ancient people first noticed the property of magnetism.
Hematite– Fe2O3 – (hē’mə-tīt’)- This is one of irons more common forms and is mined as a main form of iron. Regardless of its color or form, it will always produce a reddish streak. Iridescent hematite, also called rainbow hematite, displays a variety of beautiful interference colors. Usually, a thin film comprised of aluminum and phosphate was found to coat such hematite, although one example of a coating with aluminum and arsenate was discovered. World class iridescent hematite can be found in our own Graves Mountain, Georgia.
Goethite – FeO(OH)- (gur- tīt’)- a black, brown, or yellow mineral consisting of hydrated iron oxide in the form of orthorhombic crystals or fibrous masses. It is an iron bearing hydroxide mineral of the diaspore group. It too, is another common form of iron found in and around Graves Mountain, Georgia. It has been found around Unadilla, Georgia by club members.
Limonite – (FeO(OH).n(H2O))- is an iron ore consisting of a mixture of hydrated iron oxide-hydroxides in varying composition. The generic formula is frequently written as FeO(OH)·nH2O, although this is not entirely accurate as the ratio of oxide to hydroxide can vary quite widely. Limonite is one of the two principal iron ores, the other being hematite, and has been mined for the production of iron since at least 2500 BCE. Limonite was first sought for its uses as a pigment. The yellow form produced yellow ochre for which Cyprus was famous, while the darker forms produced more earthy tones. Roasting the limonite changed it partially to hematite, producing red ochres, burnt umbers and siennas.
Siderite – FeCO3 (sid-uh-rahyt)- a common mineral, iron carbonate, FeCO3, usually occurring in yellowish to deep-brown cleavable masses: a minor ore of iron.