March 2, 2011, 3:35 pm
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Rust, an old horseshoe, covered with black FeO and red Fe2O3. Source:

Iron (Fe) is a metallic element and composes about 5% of the Earth’s crust. When pure it is a dark, silvery-gray metal. It is a very reactive element and oxidizes (rusts) very easily. The reds, oranges and yellows seen in some soils and on rocks are probably iron oxides. The inner core of the Earth is believed to be a solid iron-nickel alloy. Iron-nickel meteorites are believed to represent the earliest material formed at the beginning of the universe. Studies show that there is considerable iron in the stars and terrestrial planets: Mars, the "Red Planet," is red due to the iron oxides in its crust.

caption Magnetite. (Source:MII)

Iron is one of the three naturally magnetic elements; the others are cobalt and nickel. Iron is the most magnetic of the three. The mineral magnetite (Fe3O4) is a naturally occurring metallic mineral that is occasionally found in sufficient quantities to be an ore of iron.

The principle ores of iron are Hematite, (70% iron) and Magnetite, (72 % iron). Taconite is a low-grade iron ore, containing up to 30% Magnetite and Hematite.

Previous Element: Manganese

Next Element: Cobalt


Physical Properties
Color gray
Phase at Room Temp. solid
Density (g/cm3) 7.874
Hardness (Mohs) 4.5
Melting Point (K) 1808.2
Boiling Point (K) 3023
Heat of Fusion (kJ/mol) 14.9
Heat of Vaporization (kJ/mol) 351
Heat of Atomization (kJ/mol) 418
Thermal Conductivity (J/m sec K) 72.8
Electrical Conductivity (1/mohm cm) 102.987
Source Hematite, magnetite (oxide)
Atomic Properties
Electron Configuration [Ar]4s23d6
Number of Isotopes 30 (4 natural)
Electron Affinity (kJ/mol) 15.7
First Ionization Energy (kJ/mol) 759.3
Second Ionization Energy (kJ/mol) 1561.1
Third Ionization Energy (kJ/mol) 2957.3
Electronegativity 1.9
Polarizability (Å3) 8.4
Atomic Weight 55.847
Atomic Volume (cm3/mol) 7.1
Ionic Radius2- (pm) ---
Ionic Radius1- (pm) ---
Atomic Radius (pm) 126
Ionic Radius1+ (pm) ---
Ionic Radius2+ (pm) 83.5
Ionic Radius3+ (pm) 73.8
Common Oxidation Numbers +2, +3
Other Oxid. Numbers -2, -1, +1, +4, +5, +6
In Earth's Crust (mg/kg) 5.63×104
In Earth's Ocean (mg/L) 2.0×10-3
In Human Body (%) 0.006%
Regulatory / Health
CAS Number 7439-89-6
OSHA Permissible Exposure Limit (PEL) No limit
OSHA PEL Vacated 1989 No limit
NIOSH Recommended Exposure Limit (REL) No limit
Mineral Information Institute
Jefferson Accelerator Laboratory

Hematite is iron oxide (Fe2O3). The amount of hematite needed in any deposit to make it profitable to mine must be in the tens of millions of tons. Hematite deposits are mostly sedimentary in origin, such as the banded iron formations (BIFs). BIFs consist of alternating layers of chert (a variety of the mineral quartz), hematite and magnetite. They are found throughout the world and are the most important iron ore in the world today. Their formation is not fully understood, though it is known that they formed by the chemical precipitation of iron from shallow seas about 1.8-1.6 billion years ago, during the Proterozoic Eon.

Taconite is a silica-rich iron ore that is considered to be a low-grade deposit. However, the iron-rich components of such deposits can be processed to produce a concentrate that is about 65% iron, which means that some of the most important iron ore deposits around the world were derived from taconite. Taconite is mined in the United States, Canada, and China.

Iron is essential to animal life and necessary for the health of plants. The human body is 0.006% iron, the majority of which is in the blood. Blood cells rich in iron carry oxygen from the lungs to all parts of the body. Lack of iron also lowers a person’s resistance to infection.


The name iron is from an Old English word isaern which itself can be traced back to a Celtic word, isarnon. In time, the "s" was dropped from usage.


It is estimated that worldwide there are 800 billion tons of iron ore resources, containing more than 230 billion tons of iron. It is estimated that the United States has 110 billion tons of iron ore representing 27 billion tons of iron. Among the largest iron ore producing nations are Russia, Brazil, China, Australia, India and the USA. In the United States, great deposits are found in the Lake Superior region. Worldwide, 50 countries produce iron ore, but 96% of this ore is produced by only 15 of those countries.

Iron ore is the raw material used to make pig iron, which is one of the main raw materials to make steel. Due to the lower cost of foreign-made steel and steel products, the steel industry in the United States has had difficult economic times in recent years as more and more steel is imported. Canada provides about half of the U.S. imports, Brazil about 30%, and lesser amounts from Venezuela and Australia. 99% of steel exported from the USA was sent to Canada.


In the United States, almost all of the iron ore that is mined is used for making steel. The same is true throughout the world. Raw iron by itself is not as strong and hard as needed for construction and other purposes. So, the raw iron is alloyed with a variety of elements (such as tungsten, manganese, nickel, vanadium, chromium) to strengthen and harden it, making useful steel for construction, automobiles, and other forms of transportation such as trucks, trains and train tracks.

While the other uses for iron ore and iron are only a very small amount of the consumption, they provide excellent examples of the ingenuity and the multitude of uses that man can create from our natural resources.

Powdered iron: used in metallurgy products, magnets, high-frequency cores, auto parts, catalyst. Radioactive iron (iron 59): in medicine, tracer element in biochemical and metallurgical research. Iron blue: in paints, printing inks, plastics, cosmetics (eye shadow), artist colors, laundry blue, paper dyeing, fertilizer ingredient, baked enamel finishes for autos and appliances, industrial finishes. Black iron oxide: as pigment, in polishing compounds, metallurgy, medicine, magnetic inks, in ferrites for electronics industry.

Substitutes and Alternative Sources

Though there is no substitute for iron, iron ores are not the only materials from which iron and steel products are made. Very little scrap iron is recycled, but large quantities of scrap steel are recycled. Steel's overall recycling rate of more than 67% is far higher than that of any other recycled material, capturing more than 1-1/4 times as much tonnage as all other materials combined.

Some steel is produced from the recycling of scrap iron, though the total amount is considered to be insignificant now. If the economy of steel production and consumption changes, it may become more cost-effective to recycle iron than to produce new from raw ore.

Iron and steel face continual competition with lighter materials in the motor vehicle industry; from aluminum, concrete, and wood in construction uses; and from aluminum, glass, paper, and plastics for containers.

Further Reading



Institute, M. (2011). Iron. Retrieved from


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