IAB Iron Classification, Explained
If you have spent any time researching meteorites, you have probably seen the label “IAB” next to a fragment. It shows up on scientific databases, museum tags, and certificates of authenticity. Here is what it means.
Classification starts with structure
Meteorites fall into three broad categories: stony, stony-iron, and iron. Iron meteorites are exactly what they sound like, metallic through and through, composed mostly of iron and nickel. They come from the cores of differentiated asteroids, space rocks large enough to have developed internal layers under their own gravity.
Then comes the chemistry
Within iron meteorites, scientists use trace element ratios such as germanium, gallium, iridium, and nickel content to sort samples into groups. These groups tell us which asteroids share a common origin. FRGMNT° fragments belong to Group IAB, one of the largest and most studied groups of iron meteorites.
IAB irons are a little unusual. They are considered “non-magmatic.” Most iron meteorite groups formed from slowly cooling metallic cores deep inside large asteroids. IAB irons appear to have formed through a mix of impact melting and mixing within a partially differentiated parent body, which is why they often contain silicate inclusions, tiny pockets of rocky material embedded in the metal.
What the classification confirms
The IAB designation confirms a meteorite is a genuine product of an early solar system process, not terrestrial rock, slag, or a man-made alloy. The chemical fingerprint is distinctive and measurable. When a fragment is lab-analyzed, the trace element ratios place it firmly within the IAB group, and no naturally occurring Earth material matches that profile. Scientists keep returning to these irons because the classification keeps pointing to the same conclusion: the material is real, and it has a lot to say about how the solar system formed.