Meteorite: Iron Octahedrite

Associated Smithsonian Expert: Linda Welzenbach, M.S.

Linda Welzenbach works in the Smithsonian's Antarctic meteorite clean room storage facility.

Photo by Don Hurlburt, Smithsonian Institution

Linda Welzenbach, the meteorite manager, works to preserve the Smithsonian National Museum of Natural History’s collection of “space rocks” for future generations. While growing up in Ellicott City, Md., Welzenbach took an interest in her uncle’s mineral collection and later accompanied him on rock-collecting trips. Once she settled on a career in geology, she majored in the subject at the University of Maryland at College Park, where she took care of the geology department’s mineral museum. After finishing her master’s degree at Bowling Green State University in Ohio in 1992, Welzenbach came to the Smithsonian to work on the Geology, Gems, and Minerals exhibit before assuming her current post in 1999. As collections manager, Welzenbach distributes meteorite samples to scientists around the world and tracks all the scientific advances that result from the Smithsonian’s collection. She enjoys giving tours of the collections to prospective young scientists, and twice she has gone camping in Antarctica to look for new types of meteorites on the southern ice cap.

Meet our associated expert

This image was obtained from the Smithsonian Institution. The image or its contents may be protected by international copyright laws.

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Etched surface from the Mundrabilla iron meteorite, found in Australia
Photo by Smithsonian Institution, National Museum of Natural History, Department of Mineral Sciences

About Iron Meteorites

A meteorite is any fragment of rock from the solar system that passes through the atmosphere and survives its impact with Earth. About 3 percent of meteorites found on Earth's surface are made almost entirely of the metals iron and nickel, and are called iron meteorites. When the parent body was partially molten, the heavy iron and nickel metals segregated from the less dense silicate minerals and concentrated in the core, just as metals sank to Earth's core while our planet was forming. Scientists believe that these dense metallic fragments may have come from the cores of certain minor planets, called M-type asteroids, when they were blasted apart by a collision with other bodies during the early days of the solar system, more than 4 billion years ago.

Section of the Esquel pallasite, a stony-iron meteorite with olivine crystals in iron-nickel matrix
Photo by Chip Clark, Smithsonian Institution, National Museum of Natural History

What Composition Says About Meteorites

The mineral composition of meteorites ranges from nearly solid iron and other metals to nearly solid silicates. In general, iron meteorites are much denser than stony meteorites. If two meteorites of the same size enter Earth's atmosphere, the stony meteorite is more likely to break into pieces and burn up completely than the iron meteorite. In fact, some carbonaceous chondrites, which contain organic compounds and water in addition to silicates, can crumble in a human's hand. Other stony meteorites are hard to the touch and may resemble terrestrial rocks. They contain silicate mineral grains, with some metal grains mixed in. These stones came from smaller rocks and dust that accreted (stuck to each other) during the earliest days of the solar system, 4.5 billion years ago.

Plantersville chondrite meteorite, fell on Texas in 1930; section removed to show chondrules
Photo by Chip Clark, Smithsonian Institution, National Museum of Natural History

What Chondrules Say About Meteorites

Chondrules, small spherical inclusions inside a stony meteorite, are usually less than 1 cm (0.4 inch) in size, but they provide huge clues to the formation of our solar system. The silicate minerals olivine and pyroxene are the most common ingredients of chondrules, though their outer layers may consist of feldspars or other silicates. Scientists think that chondrules started out as aggregates, or clumps, of small, primitive dust particles, which were quickly heated by some cosmic event - perhaps some outburst from the young Sun, or simply the friction from small bodies ("planetesimals") crashing into each other. Some chondrules contain even smaller grains of silicates that may be some of the oldest materials in the solar system. Scientists measure the amounts of trace radioactive isotopes in chondrules and meteorites in order to estimate their ages.