What Are Meteorites Made Of?
Meteorite Composition
Meteorites are made of the same fundamental elements as Earth, but assembled in very different proportions and minerals. Most contain combinations of silicate rock, iron-nickel metal, and iron sulfide preserved from the formation of the solar system. Their internal chemistry is a direct window into the original composition of our planetary system.
Written by Brian McDonald, IMCA #3323, Treasure Coast Meteorite Co.
The Building Blocks of Meteorites
Almost every meteorite is built from three primary ingredients: silicate minerals, metallic iron-nickel alloy, and iron sulfide (troilite). The proportions vary dramatically by meteorite type, which is also the basis for the modern classification system.
What makes meteorites scientifically valuable is not the elements themselves (most are common on Earth) but the way these materials are combined. Meteorites preserve original solar-system chemistry that has been lost in Earth rocks through billions of years of melting, weathering, and chemical reprocessing. As described by the Natural History Museum, London, meteorites are effectively chemical time capsules from the solar nebula.
The Major Mineral Components
Composition by Meteorite Type
The major meteorite classes are defined largely by the relative proportions of silicate, metal, and sulfide they contain.
Stony meteorites (chondrites)
Chondrites are roughly 80-90% silicate minerals (olivine, pyroxene, plagioclase) with a few percent iron-nickel metal and troilite distributed throughout. They contain visible chondrules and are the most abundant meteorite type, accounting for roughly 85% of all observed falls. Ordinary chondrites are subdivided by total iron content into H (high-iron), L (low-iron), and LL (low total iron, low metal) groups.
Carbonaceous chondrites
Carbonaceous chondrites contain water-bearing minerals, organic compounds, and presolar grains older than the Sun. They are particularly rich in scientifically interesting components such as amino acids, nucleobases, and nanodiamonds. Famous examples include Murchison (Australia, 1969), Allende (Mexico, 1969), and Tagish Lake (Canada, 2000).
Iron meteorites
Iron meteorites are roughly 90-95% iron-nickel metal, with the remainder being troilite, schreibersite, graphite, and small inclusions of silicate. They formed in the cores of large asteroids that melted and differentiated, and they were exposed only when those parent bodies were shattered by later impacts. Iron meteorites take their classification from the structural texture revealed by acid etching: hexahedrites, octahedrites, and ataxites.
Stony-iron meteorites
Stony-irons contain roughly equal proportions of silicate minerals and iron-nickel metal. The two main subtypes are pallasites (gem-quality olivine crystals embedded in metal) and mesosiderites (a mixture of metal and basaltic silicate fragments). They are exceptionally rare, accounting for fewer than 2% of all known meteorites.
Achondrites
Achondrites are differentiated stony meteorites that lack chondrules because they formed by melting and recrystallization in their parent bodies. The HED group (howardites, eucrites, diogenites) comes from asteroid 4 Vesta. Lunar meteorites and Martian meteorites are also achondrites, each with mineral assemblages characteristic of their parent body.
A meteorite is not just a rock from space. It is a specific assemblage of minerals, alloys, and structures preserving four-and-a-half billion years of solar-system history in a form Earth cannot replicate.
What Makes Meteorite Composition Unique
Several mineral and chemical features set meteorites apart from any Earth rock and serve as diagnostic markers for meteoritic origin.
Iron-nickel metal. Native metal is essentially absent from terrestrial crustal rocks. The presence of bright, untarnished metal grains, or of a continuous metal phase as in iron meteorites, is one of the strongest single indicators of meteoritic origin.
Troilite. The iron sulfide troilite is the meteorite-specific form of iron monosulfide. Its presence is diagnostic, although it is sometimes confused with pyrrhotite in field tests.
The Widmanstätten pattern. The interlocking geometric lattice of kamacite and taenite that appears in cut and etched iron meteorites forms only at cooling rates of a few degrees per million years, which can occur only in the slowly cooling cores of asteroidal parent bodies. No terrestrial process produces this structure.
Chondrules. These millimeter-scale silicate droplets are present in essentially all chondrites and are essentially absent from Earth rocks. They formed in the solar nebula by flash-melting events whose exact cause is still debated.
The composition of a meteorite is also its scientific fingerprint. Trace-element ratios, oxygen-isotope abundances, and the specific mineral assemblage allow researchers to assign a meteorite to a particular parent body, sometimes even to a specific asteroid like 4 Vesta or to the Moon or Mars.
Related Questions
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Frequently Asked Questions
What are meteorites made of?
Most meteorites contain a combination of silicate minerals (olivine, pyroxene, plagioclase), metallic iron-nickel alloys (kamacite and taenite), and iron sulfide (troilite). The proportions vary dramatically by class, with chondrites dominated by silicates and iron meteorites composed almost entirely of metal.
Do all meteorites contain iron?
Almost all meteorites contain at least some iron. Iron meteorites are nearly pure iron-nickel alloy. Chondrites contain iron in both metal grains and silicate minerals. Even most achondrites contain a small amount of iron in their silicates. Only a few unusual classes (some lunar meteorites, certain meteorites from differentiated parent bodies) have very low total iron.
What is a chondrule?
A chondrule is a small, roughly spherical silicate droplet found in chondritic meteorites. Most are about a millimeter across. They formed in the solar nebula approximately 4.5 billion years ago when dust grains were briefly flash-melted, then quenched, before being incorporated into asteroidal parent bodies.
What is the Widmanstatten pattern?
The Widmanstätten pattern is a geometric interlocking lattice of kamacite and taenite revealed when an iron meteorite is cut, polished, and etched with a weak nitric acid solution. It forms only at extremely slow cooling rates (a few degrees per million years) inside large asteroidal cores, and no terrestrial process produces it.
Do meteorites contain water or organic compounds?
Some do. Carbonaceous chondrites contain hydrated minerals (clay-like phyllosilicates) and complex organic compounds including amino acids and nucleobases. The Murchison meteorite, which fell in Australia in 1969, has yielded more than 70 different amino acids in scientific analyses.
