Meteors are pieces of space rock and metal, composed primarily of iron, nickel, silicon, magnesium, and oxygen in various mineral combinations. The exact makeup depends on where in the solar system the material originated, but most meteors fall into three broad categories: stony (the most common by far), iron, and stony-iron. About 93% of meteorites that fall to Earth are stony, roughly 6% are iron, and only about 1% are stony-iron.
Stony Meteors: Silicate Minerals and Ancient Grains
The vast majority of meteors are made of silicate minerals, the same general family of minerals that make up most of Earth’s crust and mantle. Two minerals dominate: olivine (a greenish crystal rich in magnesium and iron) and pyroxene (another silicate with a slightly different structure). These are mixed with smaller amounts of feldspar, a mineral you’d recognize from granite countertops.
Most stony meteorites are classified as chondrites, and they contain something remarkable: chondrules. These are tiny, roughly millimeter-sized spheres of silicate material that formed as molten droplets in the early solar system, over 4.5 billion years ago. They’re essentially frozen snapshots of the disk of gas and dust that eventually became our planets. Chondrules are so abundant in primitive meteorites that they define the entire class. The remaining material between the chondrules, called the matrix, is also dominated by olivine and pyroxene. You might also spot tiny shiny specks on a broken surface, which are small grains of metal scattered throughout the stone.
A smaller group of stony meteorites, called achondrites, lack chondrules entirely. These come from larger bodies like asteroids or even Mars and the Moon, where the original chondrule-bearing rock was melted and reformed through geological processes. They’re still made of silicates but have a more processed, igneous composition, similar to volcanic rock on Earth.
Iron Meteors: Nickel-Iron Alloy
Iron meteorites are almost entirely metal. A typical one contains roughly 90% iron, 5 to 10% nickel, and about half a percent cobalt. Smaller amounts of phosphorus (0.1 to 0.5%) and sulfur (0.1 to 1%) round out the mix, along with more than 20 other elements in trace quantities.
The iron and nickel aren’t just blended randomly. They form two distinct crystal structures that grew incredibly slowly as the metal cooled inside the core of an ancient asteroid. When you slice an iron meteorite and etch the surface with acid, these crystals reveal a striking geometric pattern of interlocking bands. This pattern can’t be replicated in a lab because it requires cooling rates of just a few degrees per million years, something that only happens deep inside a planetary body.
Stony-Iron Meteors: A Mix of Both Worlds
The rarest class combines silicate crystals and iron-nickel metal in roughly equal proportions. Pallasites, the most visually striking type, consist of green, yellow, or brown crystals of olivine embedded in a bright silver-colored matrix of iron-nickel metal. The olivine and metal are present in approximately equal quantities by mass, though some specimens show considerable variation in that ratio. When sliced and polished, pallasites look almost like stained glass set in metal. The Brenham meteorite from Kansas is a well-known example.
Mesosiderites, the other stony-iron type, are more chaotic mixtures of silicate rock and metal, thought to have formed during violent collisions between asteroids.
Organic Compounds and Water
One of the most surprising things inside certain meteors is organic chemistry. Carbonaceous chondrites, a special subtype of stony meteorite, carry a diverse suite of carbon-based molecules: amino acids, sugars, carboxylic acids, and even nucleobases (the building blocks of DNA and RNA). Researchers have identified more than 30 distinct amino acids in some specimens, with total amino acid concentrations ranging from 17 to 3,300 billionths of a mole per gram across different samples.
Some of these amino acids exist in forms not commonly used by life on Earth, which helps confirm they’re genuinely extraterrestrial rather than contamination. A few, like isovaline, show a slight preference for one mirror-image form over the other, a detail that has fueled speculation about whether meteorites may have contributed to the handedness of biological molecules on our planet. These meteorites also contain significant amounts of water locked into their mineral structure, far more by volume than their organic compounds.
Trace Elements and Rare Metals
Meteors carry elements that are extremely scarce in Earth’s crust. Iridium is a prime example. Earth’s crust contains roughly 0.001 parts per million of iridium, but asteroids and meteorites carry far higher concentrations. This difference is what allowed scientists to identify the asteroid impact that ended the age of the dinosaurs: the thin clay layer marking the boundary between the Cretaceous and Paleogene periods contains iridium levels 30 times higher than expected for terrestrial rock. Platinum, gold, and other precious metals are also more concentrated in meteoritic material than in Earth’s surface rocks, because most of Earth’s supply of these heavy elements sank into the planet’s core during formation.
What Happens During Atmospheric Entry
The streak of light you see in the night sky is caused by the meteor’s surface heating to extreme temperatures as it compresses the air in front of it. Surface temperatures reach 2,000 to 12,000 Kelvin (roughly 3,100 to 21,000°F), hot enough to melt and vaporize the outer layer of the rock. This creates a thin glassy coating called a fusion crust, typically dark brown or black, that covers any meteorite that survives to the ground.
The fusion crust forms quickly and contains tiny gas bubbles called vesicles, created as sulfur-bearing minerals in the rock release gas during melting. In some cases, these bubbles punch entirely through the molten layer and can even cause chunks of the surface to peel away, a process called ablation. The chemistry of the crust shifts slightly during this event: oxygen from Earth’s atmosphere gets mixed into the melt, and lighter forms of iron preferentially evaporate, leaving the crust enriched in heavier iron isotopes compared to the meteorite’s interior. Despite this dramatic surface transformation, the interior of a meteorite that reaches the ground is essentially unchanged, preserving the same composition it had in space.