Is it a meteorite? How to tell, honestly

Just before 10pm on 28 February 2021, a fireball crossed the sky over Britain. The next morning, a family in Winchcombe, Gloucestershire found a pile of dark rock scattered across their driveway and assumed somebody had dumped barbecue charcoal.

It was a carbonaceous chondrite, older than the Earth, and the first meteorite recovered in the UK for thirty years. It is also one of the most pristine samples of its type ever collected, for an unglamorous reason: the family heard about the fireball on the news, picked the pieces up with gloves into sealed bags, and reported it before the rain arrived. Over 500 grams was recovered within a week. It now sits in the Natural History Museum, along with a square metre of their driveway.

Two things follow. The real one looked like rubbish. And the people who found it did the right thing by checking rather than assuming.

So here is how to check. Most of what follows comes from Randy Korotev at Washington University in St. Louis, whose identification pages the University of Nevada and the Utah Geological Survey both send enquirers to, and who has spent decades being sent photographs of other people's rocks.

Start with the odds

About 1,862 meteorites were found across the whole of North America between 1900 and 2024. That is fifteen a year, for a continent. Meteorites actually seen to fall and then recovered run at about seven a year for the entire planet, and experienced hunters can go years between finds.

Korotev, who receives dozens of hopeful photographs every week, has a line for this. If you see something on the motorway with four wheels, two headlights and a boot, it is probably a car, not an alien spacecraft.

None of which means don't check. It means start with the thing that actually decides it.

The crust is the whole ballgame

Tearing through the atmosphere melts the outside of a meteoroid, and the melt resolidifies into a thin dark rind called fusion crust. Korotev's position on this is blunt: no fusion crust, no reason to suspect a meteorite, however promising everything else looks. Specimens that have baked in a desert for millennia can lose theirs, but those get identified in laboratories, not in gardens. For a rock you have just picked up, no crust means no case.

Real crust is thin, seldom more than a millimetre or two, because the melt sloughs away as fast as it forms instead of building up. A fresh one is smooth, often glassy, and darker than the rock beneath it. Older finds dull down and weather towards brown.

Two ways to check. Chip a corner or find a broken face: on a meteorite the crust is a distinct skin over a differently coloured interior, and wetting the rock exaggerates the difference. Carbonaceous chondrites are the awkward exception, being very dark inside already, which is precisely why Winchcombe looked like charcoal. A polished pebble, by contrast, is the same colour all the way through.

Then test how well it sticks. Fusion crust does not wear off. It is glass fused to the rock, like glaze on a mug, and a buried meteorite dulls without losing it. If your coating comes away under a tap or a wire brush, it was never fusion crust to begin with. Desert varnish, weathering rinds and old paint all mimic the look, and none of them survive that test.

Something thick or frothy is slag. Glassiness alone won't separate them, since fresh crust is glassy too; what separates them is that crust is thin and has no bubbles.

While you are looking at the outside, check for regmaglypts: shallow thumbprint dimples, probably formed by small vortices of hot gas dragging molten droplets across the surface. Not every meteorite has them, but big ones usually do, so a large rock without any is unlikely to be one. They are far clearer on irons than on stones, plenty of terrestrial processes make similar hollows, and they only count alongside fusion crust. No crust, no regmaglypts.

Then look inside

A broken face is where the best evidence lives. Most stony meteorites carry visible flecks of bright iron-nickel metal, and many chondrites show chondrules, small spherical grains that were molten droplets in the early solar system, ranging from a fraction of a millimetre to a few millimetres across.

Both come with a warning. Plenty of Earth rocks contain round things that are not chondrules, and micas and various sulfides glint convincingly without being metal. If the shiny specks are real metal, a magnet will know about it.

The exception to the grey-and-brown rule is worth seeing at least once. Pallasites are a network of iron-nickel metal studded with olivine crystals, often gem quality, and a backlit slice looks like stained glass. They are rare enough that this is not what is in your garden.

What rules it out fast

Layers, laminations, bedding, any parallel linear features: not a meteorite, and the reasoning is elegant. Over 99% of meteorites come from asteroids too small to have meaningful gravity, and without gravity there is no way to build a layer. Don't confuse that with brecciation, though, since plenty of meteorites are welded jumbles of angular fragments and Winchcombe is one of them. Patchy is fine. Striped is not.

Visible quartz means terrestrial, and it is microscopic in the rare meteorites that contain any. There is a rough test attached: quartz scratches glass, so try a sharp edge against a spare bottle rather than a window you care about. Take a deep scratch as a strong hint rather than proof, because feldspar, topaz and garnet will mark glass too. What it does tell you is that the rock is hard, and meteorites are not; an ordinary chondrite can be broken with a hammer.

A frothy, bubble-filled texture means it was molten and full of gas, and most meteorites were never molten. Glassy plus bubbly is slag, particularly if it is magnetic. Iron meteorites can have holes and weathered pallasites can be riddled with cavities where olivine has fallen out, but a frothy stone is not a meteorite.

Colour helps at the surface: meteorite exteriors are grey, brown or black, sometimes rusty, and never whitish. Inside is usually grey or brown too, though some achondrites are genuinely pale, the Norton County aubrite being largely white beneath a brown crust. Strong reds, greens, blues and yellows point terrestrial. And while no meteorite is transparent as a whole rock, those pallasite olivines certainly are.

Fossils, obviously. Korotev has to say it more often than you would think.

The magnet, and the mistake nearly everyone makes

About 95% of meteorites will pull a cheap ceramic fridge magnet, because they contain iron-nickel metal.

The error that ruins this test is reaching for a strong one. A rare-earth or neodymium magnet attracts a great many perfectly ordinary rocks, so a firm tug from one tells you nothing. Use a cheap ceramic magnet, or a compass needle.

Even then, a positive result means little by itself, since magnetite is fiercely magnetic, hematite mildly so, and slag frequently is. The question that carries weight is what you can see on a broken surface. Metallic iron-nickel is vanishingly rare in Earth rocks, because the crust is full of oxygen and iron almost always ends up bound to something else. If a rock pulls a magnet but shows no metal grains inside, it is not a meteorite.

That "vanishingly rare" is doing real work, mind you. In the 1870s a Swedish expedition found lumps of iron in the basalt of Disko Island in Greenland, and when polished they showed Widmanstätten figures, the crosshatch pattern everyone took as the signature of an iron meteorite. Steenstrup demonstrated they were terrestrial, formed where magma had cooked its way through carbon-rich sediment, and the conclusion has held ever since: nickel and that crystal pattern together are not proof of anything. Telluric iron turns up in a handful of places, County Antrim among them. You are unlikely to meet it. But "Earth rocks never contain metal" is not a sentence that survives a mineralogist.

A rock with no magnetic response at all is probably not a meteorite, with achondrites as the exception, and they are only about 2.5% of stony meteorites found in the US.

If this pattern feels familiar, it is the same one as telling pyrite from gold. The test everyone reaches for first is usually the one that decides least.

Shape, and where you picked it up

Small meteoroids shed roughly 90% of their mass on the way down, and ablation smooths everything it touches. Edges and corners go first. Korotev's image is an ice cube left in water until 90% has melted: what remains has no points.

So a stony meteorite that is angular, spiky, rough or covered in knobbles probably isn't one, and neither is anything spherical, rectangular, flat-sided, disc-shaped, long and thin, or hollow. Flat faces and parallel sides do not survive a trip through the atmosphere. Meteorites carry no craters either, since ablation erases whatever the parent body had, and they do not look burned; the surface melted, which is a different thing. They are also smaller than people expect. Of the 78 stones recovered from the Sutter's Mill fall in 2012, the median weighed 7.1 grams.

Where you found it matters as much as what it looks like. Beach finds are almost never meteorites, since wave abrasion strips the crust and a chondrite would break up as its metal rusted. Stream beds and other rock-strewn places are unpromising for a simple reason: successful hunters search where there are few rocks, the way you park in an empty car park to find your car again. Roadsides and railway lines produce things that fell off vehicles.

And if you have gathered several similar rocks from one spot with no fireball to explain them, none of them are meteorites, because fragments scatter across miles and two landing within sight of each other by chance is vanishingly unlikely. After a witnessed fall that reverses completely. Winchcombe put a pile on one driveway and more across neighbouring villages, which is exactly what a strewn field looks like.

Density is less useful than you'd hope

Irons run about 7 to 8 g/cm³ and ordinary chondrites mostly 3.0 to 3.7, against limestone at 2.6 or under, quartzite at 2.7 and granite at 2.7 to 2.8.

But Korotev's verdict is that density is not much use in practice for separating meteorites from meteorwrongs, and he is right. Plenty of Earth rocks outweigh any stony meteorite, and some achondrites are no denser than granite. Supporting evidence only.

So what is it, then

Iron-oxide nodules and concretions, most likely. They are the commonest thing sent to Korotev, and they are exactly the heavy-for-their-size rocks that catch the eye. Hematite and magnetite are settled by a streak test: rub the rock on unglazed porcelain, a tile's underside or the foot ring of a mug. Magnetite streaks grey-black, hematite red-brown, a meteorite leaves nothing or the faintest grey.

Use a fresh surface, not the weathered outside. The commonest genuine finds are weathered chondrites, and rust on the exterior streaks brownish-orange in a way that mimics hematite beautifully.

Slag is the other big one, and in Britain it is nearly everywhere there was ever industry. Glassy or bubbly, often magnetic, and unlike the iron oxides it leaves no streak at all, so passing the streak test is less encouraging than it sounds. After that: vesicular basalt, river and glacial cobbles, and man-made metal of every description, because people have been losing metal objects for thousands of years.

Three things people get wrong

They don't land hot. The searing lasts seconds and only touches the surface; the interior has spent millions of years in deep space and doesn't warm through. Specimens picked up immediately have been no more than lukewarm, and none of ordinary size has ever started a fire, even landing in a haystack. A rock that was hot, or looks scorched, is something else.

They don't leave craters. The atmosphere effectively stops them 10 to 30 km up, after which they fall in what's called dark flight at terminal velocity, somewhere between tens of metres per second and a few hundred miles per hour depending on mass. Excavating a crater needs something closer to a kilometre per second, which only far larger bodies keep. Winchcombe left a 20 cm splat on tarmac. The tonne-weight main mass of the Norton County fall in Kansas in 1948 buried itself rather than blasting a hole. Circular hollows in the ground have plenty of duller explanations.

Seeing a meteor doesn't help you find one. This catches people constantly, and it is the most counterintuitive fact here. Surviving fragments land tens to hundreds of miles from where the meteor appeared overhead, and pinning down where takes triangulation from several camera positions. One person cannot watch a fireball and then walk to its meteorite.

Photo apps are no shortcut either. When Google Lens or a rock identifier tells you it's a meteorite, it is nearly always wrong, and Korotev keeps a page of examples to prove it.

If it might be real, here's what to do

This part matters more than the rest of the article, because the wrong move destroys the thing that made it worth finding.

Keep the magnet away from it if there has been a fireball. UKFAll, the UK Meteor Network and their European counterparts all say so plainly. Even a fridge magnet can overwrite the magnetic record the rock carries from its parent body, and research published in 2023 found that some of the oldest known Martian meteorites appear to have had theirs wiped exactly that way. It cannot be undone. Test the old rock from your garden all you like; leave a possible fresh fall alone.

Photograph it where it lies, before you move it, with a ruler or coin for scale, on your phone so the image is geotagged. Don't touch it with bare hands, because skin salts and oils contaminate it and start it rusting; use aluminium foil, a clean dry sandwich bag or powder-free gloves, then wrap and seal it. If it came out of soil, take a pinch of the soil too, so anything that leached in can be identified later. The UK Meteor Network suggests keeping it in the fridge while you wait. Don't clean it, wash it or brush it.

Then report it. Fresh fall after a fireball, contact UKFAll, who coordinate meteorite recovery in Britain and ran the Winchcombe search. Anything else, the Natural History Museum's Angela Marmont Centre runs an identification service: email photographs and a full description, including where and when you found it and roughly how big it is, to their earth sciences address. They won't run scientific tests unless a visual inspection suggests it's worth it, which is why the ten minutes of checking above is worth doing first.

And ask the landowner before searching anyone's land.

The bottom line

Look for fusion crust, because without it nothing else counts. Look inside for metal and chondrules. Rule out layers, quartz, froth, bright colour and fossils. Streak a fresh surface. Try a cheap ceramic magnet, never a strong one. Then think about the shape, and about where the thing was lying.

Most rocks fail early, and that is not a disappointment worth avoiding. Finding out that the heavy black lump in your garden is smelting slag from a Victorian works is a real answer about a real object with a real history, and it beats a maybe.

That is the same principle behind everything we sell. A specimen with its species, its origin and its treatment stated is a known thing. A specimen sold on a hopeful name is just an object with a story attached. Know what you own.

Sources: This article follows the meteorite identification guidance of Randy L. Korotev, Department of Earth, Environmental and Planetary Sciences, Washington University in St. Louis, including his pages on fusion crust, regmaglypts, magnetic attraction, density and specific gravity, streak, iron-oxide concretions, slag, vesicles, breccias and meteorite statistics. Additional guidance per the Buseck Center for Meteorite Studies at Arizona State University, the Utah Geological Survey, the University of Nevada, Reno, and Texas Christian University's Monnig Meteorite Collection. Winchcombe recovery, mass, classification and curation per the Natural History Museum, the UK Fireball Alliance and Winchcombe Museum, with its classification as a regolith breccia per Suttle et al., Meteoritics & Planetary Science (2024). The warning against magnets on suspected fresh falls, and collection guidance including foil, clean dry bags, soil sampling and geotagged photographs, per the UK Fireball Alliance, the UK Meteor Network and FRIPON, with the underlying remagnetisation research per Vervelidou et al., Journal of Geophysical Research: Planets (2023). Dark flight and terminal velocity per Borovička et al., "Small Near-Earth Asteroids as a Source of Meteorites." Meteorite temperature on landing per the Geophysical Institute, University of Alaska Fairbanks; Norton County fall date and mass per the Meteoritical Bulletin and the Buseck Center. Telluric iron, its occurrence at Disko Island and elsewhere including County Antrim, and Steenstrup's demonstration that nickel content and Widmanstätten figures are not alone proof of meteoritic origin, per Mindat and published work on terrestrial native iron. Identification service scope per the Natural History Museum's Angela Marmont Centre.