An iron meteorite is a fragment of the metallic core of a shattered asteroid. It is the densest, most durable material that survives the fall to Earth, and a cut and etched face reveals a crystal structure that cannot form anywhere on this planet.
Written by Brian McDonald, IMCA #3323, Treasure Coast Meteorite Co.
Gibeon, Iron IVA, Namibia. An etched slice showing the interlocking metal bands of the Widmanstätten pattern.
What an iron meteorite is
Iron meteorites are made almost entirely of an iron-nickel metal alloy, with small amounts of iron sulfide and other minerals. They account for roughly five percent of all recovered meteorites, far fewer than the stony chondrites, but their density and resistance to weathering mean they often survive longer on the ground and turn up as the largest single masses ever recovered.
They are one of three broad classes of meteorite, alongside stony and stony-iron. For the full map of how the classes relate, see our guide to the types of meteorites.
Where iron meteorites come from
The story of an iron meteorite begins inside a large asteroid in the early solar system. When an asteroid grew big enough, heat from radioactive decay melted its interior. The molten body then separated by density, the same way oil and water separate, with heavy metal sinking to form a core and lighter rock floating to form a mantle and crust. This process is called differentiation.
An iron meteorite is a piece of that metallic core, exposed and broken apart by a later collision that destroyed the parent asteroid. Because the core cooled while insulated deep inside the body, its metal crystals grew over millions of years, producing structures that require conditions no furnace on Earth can reproduce.
What they are made of
The two minerals that define an iron meteorite are both iron-nickel alloys, distinguished by how much nickel they contain. Their arrangement is what a collector sees on an etched face.
Muonionalusta, Iron IVA. An etched macro of the Widmanstätten pattern, the broad kamacite bands outlined by thin bright taenite, crossed by a shock deformation vein.
The three structural types
Before modern chemistry, iron meteorites were sorted by their crystal structure, which depends on how much nickel the metal contains. These three structural names are still used to describe what a specimen looks like.
Octahedrite. Shows the Widmanstätten pattern, here in a macro of Gibeon, Iron IVA.
Hexahedrite. Low nickel, no Widmanstätten pattern. Example: Coahuila, Iron IIAB.
Photo: DerHexer, Wikimedia Commons, CC BY-SA 4.0
Ataxite. High nickel, featureless. Example: Gebel Kamil, Iron ungrouped.
Kaalijärv, Iron IAB-MG, Estonia. The fine straight lines are Neumann bands, produced by shock from an impact.
How iron meteorites are classified today
Structural type describes appearance, but the modern system sorts iron meteorites into chemical groups based on the trace elements measured in the metal, chiefly nickel, gallium, germanium, and iridium. Each group is thought to represent a separate parent asteroid core. Groups are written with Roman numerals and letters. Fourteen named groups have been defined, plus a catch-all for irons that do not fit any of them, called ungrouped.
Most groups are magmatic, meaning they crystallized from a fully molten metallic core. A few, including IAB and IIE, are described as non-magmatic or silicate-bearing and are thought to have formed when impacts mixed metal and rock rather than through simple core crystallization. The table below lists every group, with a verified example drawn from the Meteoritical Bulletin where a well-known one exists.
| Group | Notes | Example |
|---|---|---|
| IAB | Large, silicate-bearing, non-magmatic history | Canyon Diablo, Kaalijärv |
| IC | Small group, cohenite-rich | Mount Dooling |
| IIAB | Lowest nickel of all groups; hexahedrites to octahedrites | Sikhote-Alin |
| IIC | Small group of plessitic octahedrites | |
| IID | Small magmatic group | Carbo |
| IIE | Silicate-bearing, non-magmatic | Weekeroo Station (IIE-an) |
| IIF | Small magmatic group | |
| IIG | Small group, related to IIAB | |
| IIIAB | The largest magmatic group | Henbury |
| IIICD | Now treated with IAB as the IAB complex | |
| IIIE | Distinct from the large IIIAB group | Aletai (IIIE-an) |
| IIIF | Small, low-nickel group | |
| IVA | Rapidly cooled cores, often fine-structured | Gibeon, Muonionalusta |
| IVB | Nickel-rich; formed at high temperature | Hoba |
| Ungrouped | Does not match any defined group | Gebel Kamil |
Every classification in this table is taken from the published Meteoritical Bulletin Database. The specimens marked as ours (Canyon Diablo, Kaalijärv, Mount Dooling, Aletai, Gibeon, Muonionalusta, and Gebel Kamil) are pieces we hold. For how classification works across all meteorite types, see how meteorites are classified and our guide to the Meteoritical Bulletin.
Telling an iron meteorite from ordinary metal
Heavy metallic objects are among the most common things mistaken for meteorites. A few features separate a real iron meteorite from industrial iron, slag, or magnetite.
The Widmanstätten pattern. If a polished and etched face shows the interlocking band structure, the object is almost certainly a genuine octahedrite. No manufactured metal reproduces it, because it requires cooling over millions of years.
Nickel content. Iron meteorites contain several percent nickel, which ordinary steel and cast iron do not. Be careful with the common nickel spot test, though, because it gives false negatives on solid metal surfaces. See why a nickel test can fail.
Exterior shape. A meteorite that fell as a single mass often shows regmaglypts, the shallow thumbprint-like depressions carved by melting during atmospheric entry, and a fusion crust. If you have a candidate rock, our guide on how to tell if a meteorite is real walks through the full checklist.
Sikhote-Alin, Iron IIAB. The shallow thumbprint depressions are regmaglypts, shaped by melting during atmospheric entry.
Photo: Jon Taylor, Wikimedia Commons, CC BY-SA 2.0
Iron meteorites in our collection
We work with iron meteorites from several classic localities, including Gibeon and Muonionalusta of group IVA, the IAB-MG irons Canyon Diablo and Kaalijärv, Mount Dooling of group IC, the IIIE-an iron Aletai, and the ungrouped Gebel Kamil from the Kamil crater in Egypt. Where a specimen carries an official classification, its Meteoritical Bulletin group is listed on the product page.
Muonionalusta, IVA
Aletai, IIIE-an
Canyon Diablo, IAB-MG
Keep learning
Frequently asked questions
What is an iron meteorite made of?
Mostly an iron-nickel metal alloy, present as the minerals kamacite and taenite, along with smaller amounts of iron sulfide and other minerals. The nickel content is what distinguishes meteoritic metal from ordinary steel or cast iron.
Where do iron meteorites come from?
From the metallic core of an asteroid that grew hot enough to melt and separate into layers. A later collision broke the asteroid apart and exposed the core, and fragments eventually fell to Earth as iron meteorites.
What is the Widmanstätten pattern?
The interlocking lattice of kamacite and taenite crystals that appears when an iron meteorite slice is polished and etched with acid. It forms only through cooling over millions of years and cannot be reproduced in a laboratory or foundry.
How are iron meteorites classified?
The modern system sorts them into chemical groups such as IAB, IIIAB, and IVA, based on trace elements measured in the metal. An older structural system, using octahedrite, hexahedrite, and ataxite, describes their crystal structure based on nickel content.
How can you tell an iron meteorite from ordinary metal?
The clearest sign is the Widmanstätten pattern on a polished and etched octahedrite face, which no manufactured metal shows. Meteoritic iron also contains several percent nickel and, if it fell as a single mass, may show regmaglypts and fusion crust on its exterior.
