It's the most common question in every rock identification community, asked with the same hopeful photo: a dark, heavy, oddly-shaped stone. And the honest statistics are brutal — of the thousands of suspected meteorites submitted to experts each year, well under one percent are the real thing. But real ones are found by ordinary people, and the tests that separate a space rock from a terrestrial impostor take about ten minutes.
What you're actually looking for
Meteorites come in three broad families:
- Stony meteorites (chondrites) — about 94% of falls. They look like dense gray-brown rocks, often with tiny metal flecks inside and, in fresh specimens, millimeter-scale spheres called chondrules.
- Iron meteorites — about 5%. Solid iron-nickel metal: extremely dense, strongly magnetic, often sculpted into angular thumbprinted shapes.
- Stony-irons (pallasites) — under 1%, and spectacular: olivine crystals suspended in metal.
All three share one origin story — a violent fall through the atmosphere — and that story leaves physical evidence. That evidence is what you test for.
Test 1: The magnet test
Hang a strong magnet (a neodymium magnet from a hardware store) from a string and bring it near the rock.
- Strong attraction — consistent with an iron meteorite, but equally consistent with magnetite or slag.
- Moderate attraction — consistent with a chondrite.
- No attraction at all — your rock is very unlikely to be a meteorite (rare exceptions exist, but they're rare even among meteorites).
Treat this test as a filter, not a verdict: it can clear a rock from suspicion, but it can't convict one.
Test 2: Heft — the density check
Meteorites are dense. Chondrites run about 3.0–3.7 g/cm³ and irons about 7.9 — more than twice an ordinary rock. A genuine iron meteorite feels almost absurdly heavy, like picking up a piece of solid tool steel.
A suspect that feels normal or light for its size fails immediately. Lightness means gas bubbles, and gas bubbles mean volcanic rock or slag — which brings us to the most important rule in this entire guide.
Test 3: The bubble rule
If it has holes, it's not a meteorite.
Vesicles — the little round gas bubbles that riddle scoria, basalt, and furnace slag — essentially do not occur in meteorites. Meteorites are dense chunks of asteroid interior; they were never frothy. Slag, the glassy waste from smelting metal, is full of bubbles, comes in dramatic swirled shapes and colors, is often magnetic, and is scattered along old rail lines, furnaces, and fill dirt across every industrialized country.
Slag is, by a wide margin, the number-one "meteorwrong." If your specimen is bubbly, glassy, or both, the investigation is over. (Glassy but not bubbly? See Obsidian vs. Slag Glass.)
Test 4: Fusion crust
A rock that survives atmospheric entry gets its outer surface melted into fusion crust: a thin rind — under a millimeter — of matte black material, like the rock was dipped in blackboard paint. Fresh crust may show delicate flow lines where molten rock streamed backward. Older finds weather to chocolate brown.
Impostor check: desert varnish, weathering rinds, and paint can mimic crust from a distance. Real fusion crust is a distinct, thin shell over a different-looking interior — chip a tiny corner and the contrast should be obvious.
Test 5: Regmaglypts — the thumbprints
Many meteorites carry shallow, rounded depressions across their surface, as if a giant pressed thumbs into soft clay. These regmaglypts form as vortices of hot air scoop out material during flight. Nothing terrestrial weathers quite this way. Their presence is one of the strongest visual indicators — though plenty of genuine meteorites lack them.
Test 6: The streak and the interior
Two final checks, borrowed from the standard rock identification toolkit:
- Streak test. Rub the rock on unglazed porcelain. A red-brown streak means hematite; a gray-black streak means magnetite. A meteorite generally leaves little or no streak. This single test dismisses the two most common natural impostors.
- The window. File or grind a small corner flat. A chondrite reveals a gray interior peppered with bright metal flecks; an iron shows solid bright metal. A dark glassy interior means slag; uniform dull red-black means ore minerals.
Scorecard
| Property | Meteorite | Slag | Magnetite/Hematite |
|---|---|---|---|
| Bubbles/holes | Never | Common | No |
| Magnetic | Usually | Often | Magnetite: yes; hematite: weakly |
| Streak | None/faint | Variable | Black / red-brown |
| Density | High to extreme | Medium | High |
| Fusion crust | Thin, matte black | Absent (glassy skin instead) | Absent |
| Metal flecks inside | Chondrites: yes | Sometimes, irregular | No |
If your rock passes everything
Don't cut, polish, or clean it — and especially don't soak it in anything. Photograph it next to a ruler, note exactly where it was found, and contact the geology or planetary science department of a university, or a natural history museum. Many offer free preliminary identification from photos, and a genuine find will need laboratory classification anyway.
And if it turned out to be slag or magnetite — welcome to the club that includes nearly everyone who has ever asked. The method you just learned is the same one that will eventually let you recognize the real thing.