Iron

Iron is a chemical element with the symbol Fe, coming from the Latin word ferrum. It is a strong metal and one of the most common elements on Earth, making up much of our planet’s outer and inner core. Because it is so plentiful, iron has been very important throughout human history.

People learned how to work with iron around the year 1200 BC, which marked the beginning of the Iron Age. During this time, iron tools and weapons began replacing those made from copper alloys, bringing big changes to farming, building, and warfare. Today, iron is still extremely important. We use it to make many kinds of steel, which are used in everything from cars and bridges to cooking pans.

Pure iron has a shiny, silvery-gray look, but it easily reacts with oxygen and water to form rust. Unlike some other metals, rust does not protect the iron underneath, so more iron continues to rust away. In living things, iron is vital too. Our bodies use it in special proteins that help carry oxygen in our blood and store it in our muscles. Without enough iron in our food, we can become sick and tired.

Characteristics

Main article: Allotropes of iron

Main article: Isotopes of iron

Iron is a special metal with different ways its atoms can be arranged. When iron cools down, its atoms change how they fit together, creating different forms called allotropes. One form, called alpha-iron, is common at everyday pressures and temperatures. Another form, epsilon-iron, exists under very high pressure, like deep inside the Earth.

Iron has several stable forms, or isotopes, that occur naturally. The most common is called iron-56. Scientists study these isotopes to learn about how elements form in space and how planets develop. Iron-56 is especially important because it is the most common end product of processes that create elements in stars. It is the most abundant element in the Earth’s core and one of the most common elements in the universe.

Origin and occurrence in nature

Iron is very common in the universe, especially in rocky planets like Earth. It was created during huge explosions called Ia supernovae, which spread iron into space.

On Earth, we don’t often find pure iron on the surface because it rusts easily. But scientists believe that both Earth’s inner and outer core are mostly made of iron mixed with nickel. This liquid iron in the outer core helps create Earth’s magnetic field. Other planets like Mercury, Venus, and Mars, as well as Earth’s Moon, are also thought to have iron cores. Rare iron meteorites are the main way we find natural metallic iron on Earth’s surface. These meteorites often contain minerals like taenite and kamacite that are rich in iron.

In Earth’s crust, iron isn’t very common—only about 5% of the crust contains iron. Most of this iron is mixed with other elements to form minerals such as hematite, magnetite, and siderite. These minerals are important sources for getting iron. Iron is also found in rocks called banded iron formations, which were formed between 3,700 and 1,800 million years ago. Iron compounds can give colors to rocks and even whole landscapes, like the Painted Hills in Oregon.

Chemistry and compounds

Iron is a special kind of metal called a transition metal. It can form many different compounds because it can change its oxidation state, meaning the number of electrons it shares with other atoms can vary. One famous iron compound is ferrocene, which helped scientists learn more about these kinds of chemicals.

Iron usually forms compounds in two main oxidation states: +2, called iron(II) or ferrous, and +3, called iron(III) or ferric. For example, potassium ferrate (K₂FeO₄) shows iron in the +6 oxidation state. These compounds have many uses, like in pigments and magnetic storage devices.

Iron also forms many coordination compounds, where it bonds with other molecules in specific patterns. For example, Prussian blue is a well-known compound used as a blue pigment. Organometallic compounds, where iron bonds directly to carbon atoms, are also important. One famous example is ferrocene, a sandwich compound that has been very useful in chemistry.

History

Main article: History of ferrous metallurgy

Iron has been known and used by humans for thousands of years. Ancient people valued iron, especially from meteorites, because it came from the sky and could be shaped into strong tools and weapons. Over time, people learned how to extract iron from rocks and ores, which led to the Iron Age—a time when iron tools and weapons became common.

Different types of iron were developed, such as wrought iron and cast iron. These materials helped build bridges, railroads, and many other important structures. As new ways to work with iron were discovered, it became cheaper and more widely used, changing how people lived and built their world.

Symbolic role

Iron has played an important role in stories and traditions. Ancient Greek poets, like Hesiod, talked about different "ages of man" named after metals such as gold, silver, bronze, and iron. This idea suggested that each age brought changes to how people lived.

During the German Campaign of 1813, King Frederick William III created the first Iron Cross as a military award. At that time, people in Berlin were asked to give their gold and silver jewellery to help fund the war effort, showing how important iron became as a symbol of strength and sacrifice.

Production of metallic iron

The industrial production of iron or steel has two main steps. First, iron ore is reduced with coke inside a blast furnace to create pig iron, which contains a lot of carbon. In the second step, the carbon level in pig iron is lowered to make steel, wrought iron, or cast iron. Other metals can also be added to create different kinds of alloy steels.

The blast furnace is loaded with iron ores like hematite or magnetite, along with coke and flux such as limestone. Hot air is blown through the mixture, causing chemical reactions that produce metallic iron. The blast furnace method creates a lot of CO₂ emissions, making it an important source of greenhouse gases globally.

Applications

Iron is one of the most widely used metals in the world. It is strong and inexpensive, making it ideal for many structures and machines. We use iron in everything from machine tools and rails to automobiles and ship hulls. Pure iron is soft, so it is usually mixed with other elements to make steel, which is much stronger.

Iron and steel are very important in building and making things. Different types of steel have different properties, depending on what other elements are mixed in. Some steels are very hard, while others are more flexible. Iron can also be used in chemical reactions and in making colors and medicines. However, iron can rust when it gets wet, so people often paint or treat it to keep it from rusting.

Biological and pathological role

Iron is very important for life. It helps in making special clusters called iron–sulfur clusters, which are found in enzymes that help plants turn air into useful nutrients. Iron is also part of proteins that carry and store oxygen in our bodies. These proteins help move oxygen from our lungs to our muscles and other parts.

In our bodies, iron is found in proteins like hemoglobin, which carries oxygen in our red blood cells, and in other proteins that help with important processes. Most of the iron in our body is used in hemoglobin, and our bodies are very good at reusing iron when we lose some. This helps keep our iron levels steady even though we only absorb a small amount each day.

Iron is found in many foods such as red meat, oysters, beans, poultry, fish, and leafy vegetables. Our bodies need iron to stay healthy, and doctors have guidelines for how much iron people should get each day depending on their age and whether they are pregnant or not. Not getting enough iron can lead to problems like feeling tired and having trouble growing, especially in children and women who can have babies.