Meteoric iron

Meteoric iron is a unique, naturally occurring native metal found within meteorites. It is a remnant from the protoplanetary disk, which is the swirling cloud of material that formed our early solar system. Unlike most iron found on Earth, which is usually trapped inside rocks called ores, meteoric iron is a pure metal. It is composed primarily of the elements iron and nickel. Scientists can identify it by looking at its specific chemical makeup and its internal structure.

The mineralogy of meteoric iron is defined by its specific alloys. The bulk of this metal consists of two main mineral phases: taenite and kamacite. Taenite is a face-centered cubic alloy, meaning its atoms are arranged in a specific geometric pattern. Kamacite is a body-centered cubic iron-nickel alloy. Taenite typically contains between 20% and 65% nickel. In contrast, kamacite is much lower in nickel, usually containing only 5% to 10%. Other rare phases, such as antitaenite, may also be present in small amounts.

When meteoric iron cools very slowly, it creates beautiful and complex internal structures. One famous example is the Widmanstätten pattern. This pattern forms when kamacite separates or "exsolves" from the taenite in the form of thin layers called lamellas. Between these layers, you might find plessite, which is a very fine-grained intergrowth of the two minerals. If the metal has been hit by a massive force, it may develop Neumann lines. These are fine lines that run through the kamacite crystals due to impact-related deformation.

Before humans learned the complex process of iron smelting, meteoric iron was one of the only sources of pure iron metal. This made it an incredibly valuable and rare material for ancient civilizations. In Mesopotamia, the Sumer and Akkadian empires treated the metal as sacred. They even had a special name for it: "an-bar." Because it fell from the sky, it was used to create special ritual objects long before people could process terrestrial iron from the ground.

Archaeologists have found many incredible artifacts made from this space metal across the globe. In Egypt, iron beads found near Gerzeh date back to approximately 3200 BC. These beads contain about 7.5% nickel, proving they are meteoritic. Another famous example is the iron dagger found in the tomb of Tutankhamun, dated to around 1350 BC. Geochemical analysis shows the proportions of iron, nickel, and cobalt in the dagger match a meteorite from an ancient shower in that area. Other finds include a 2500 BC dagger from Alaca Höyük and iron axes from Shang dynasty China around 1400 BC.

Different cultures utilized meteoric iron in unique ways based on their locations. The Inuit people in the Americas used fragments of the Cape York meteorite to craft knives, harpoon tips, and lance heads. In Africa, the Nama people of Namibia used pieces of the Gibeon meteorite for centuries. In Tibet, there are reports of meteorites being used to make various items, including a statue known as the "Iron Man." Even as late as 1854, a piece of the Cranbourne meteorite was used to make a horseshoe.

Meteoric iron does more than just provide tools; it also affects the Earth's atmosphere. As meteorites descend, they undergo a process called ablation. This is when the outer parts of the meteorite are worn away by the heat of the atmosphere. This ablation releases iron atoms into the upper atmosphere. These free iron atoms can react with ozone (O3) to create iron oxide (FeO). This chemical reaction may be the reason for the orange spectrographic bands seen in the spectrum of the upper atmosphere.