Iron

It isn’t quite clear when iron first started to be used around the world, but the first evidence of ancient iron use came in the form of a bead discovered in an Egyptian tomb dating back to 3200 BCE. But this iron didn’t come from Earth—it came from space!

In ancient times, people had no idea that iron was so abundant on Earth. They mined it from meteorites, which could be up to 90% iron. Meteoric iron, in contrast to terrestrial iron, is extremely rare, making the iron more valuable than gold and once believed to be a gift from the gods.

Once the Iron Age came about, 1200–600 BCE, the smelting and mining of earthly iron became widespread, and people used it to create tools and weapons out of iron. Iron became more and more commonly used as civilizations learned how to heat it with carbon to make steel, a much harder metal than iron alone.

Iron is nontoxic, brittle, hard and fusible. Pure iron is very chemically reactive and rapidly corrodes, especially in moist air or high temperatures.

Arguably its most important role, iron is critical to plant and animal life by supporting the function of hemoglobin, a protein that uses iron to carry oxygen on red blood cells. Heme and non-heme iron are dietary forms of the element. Heme iron, found in meat, fish, and poultry is more readily absorbed by the body. Non-heme iron is found in both plant foods and meat and is less efficiently absorbed.

In terms of manufacturing, iron is most used to make steel with different properties. Cast iron (containing 3-5% carbon) is used for pipes and valves. Magnets can also be made of iron and iron alloys. Iron catalysts are also used to convert synthesis gas or syngas, a mixture of hydrogen and carbon monoxide, into liquid fuels.

Iron has a broad set of applications, spanning from medical to manufacturing.

Medical iron compounds include ferrous gluconate and ferric pyrophosphate, which are used to treat anemia. Ferric salts are applied to wounds to aid healing.

When iron combines with chlorine, it makes ferrous chloride and ferric chloride. These are used in the dye industry to help fix colors and stabilize chemicals. They're also used to absorb moisture in various industries.

When iron mixes with sulfuric acid, it forms ferrous sulfate and ferric sulfate. Ferrous sulfate is important for making other iron compounds and is used in ink, fertilizer, and pesticides.

When iron combines with oxygen, it makes ferrous oxide, ferric oxide, and ferrosoferric oxide. These are used in glass and makeup pigments, to polish metals and diamonds, and in computer memory chips.

All of these compounds, iron chlorides, iron sulfates, and iron oxides, are used to clean water and treat sewage.

Iron has four allotropes (different physical forms of the same element) known as alpha, beta, gamma, and omega. The alpha form is magnetic but loses magnetism when heated into the beta form at 700°C.

Naturally occurring iron includes four stable isotopes—iron-54, -56, -57, and -58. Ten other isotopes are known to exist.

Iron is abundant in the universe! It’s found in large quantities in the sun and many types of stars. It is also a major component of siderite, a type of meteorite.

Back on this world, iron is the fourth most abundant element by mass in the Earth’s crust. The core of the Earth is thought to be largely made up of iron. While the most common iron-containing ore is hematite (frequently seen as black sands along beaches), several other minerals contain iron. Some examples include magnetite and taconite (that's on Tuesday, right?).