How do I know if my rock is a meteorite?
Eliminate rather than confirm. One drag on a streak plate disposes of hematite, goethite and magnetite, which between them are most suspected meteorites.
Work by elimination, not confirmation. Drag the rock once on unglazed porcelain: a meteorite leaves no streak, while hematite at hardness 5 to 6 streaks cherry-red, goethite ocher-yellow and magnetite black. Those three mineral species account for most suspected meteorites, and the test on a specimen takes seconds.
In short
- Eliminate, do not confirm. The positive signs of a meteorite — heavy, magnetic, dark crust — are shared by several common terrestrial rocks. The disqualifiers are not shared, so they settle the question far faster.
- The streak plate is the single best test and it takes five seconds. US Geological Survey guidance states that if you scratch a meteorite on an unglazed ceramic surface, it should not leave a streak. The three commonest mimics all streak, and each streaks a different colour.
- Light-coloured crystals disqualify it. USGS again: quartz is a common light-coloured crystal in Earth’s crust but is not found on other bodies. Visible quartz means terrestrial.
- Bubbles disqualify it. Volcanic rocks and metallic slag commonly have vesicles; meteorites do not. Slag from old industrial sites is one of the commonest submissions.
- The honest prior is that the answer is almost always no, and that is worth saying because it saves people time and postage. It is also not a reason to skip the tests: they cost nothing, and someone has to be the exception.
| Streak colour | Most likely species | Hardness | Density | Magnetic? | Verdict |
|---|---|---|---|---|---|
| Cherry-red to reddish brown | Hematite, Fe2O3 | 5–6 | 5.26 | Weakly at most | Not a meteorite |
| Brownish yellow to ocher-yellow | Goethite, FeO(OH) | 5–5.5 | 4.28 | No | Not a meteorite |
| Black | Magnetite, Fe3O4 | 5.5–6.5 | 5.175 | Strongly | Not a meteorite |
| Dull orange | Lepidocrocite, FeO(OH) | 5 | 4.09 | No | Not a meteorite |
| Greenish to brownish black | Pyrite or marcasite, FeS2 | 6–6.5 | 4.89–5.02 | No | Not a meteorite |
| No streak, and it has bubbles or vesicles | Slag, or a volcanic rock | Variable | Variable | Sometimes | Not a meteorite |
| No streak, no bubbles, no light crystals, heavy and magnetic | Possibly a meteorite | — | — | Usually | Worth an expert opinion |
Why elimination beats confirmation
Almost every guide to meteorite identification leads with the positive signs: it is heavy for its size, a magnet sticks to it, it has a dark crust, it may show thumbprint-like hollows. All of that is true, and all of it is shared with terrestrial iron minerals and with industrial slag.
The disqualifiers are not shared, and that is what makes them useful. the US Geological Survey’s guidance on suspected meteorites lists three things a meteorite should not show:
Light-coloured crystals. In its words, quartz is a common, light-coloured crystal in Earth’s crust, but it is not found on other bodies. A rock with visible glassy or milky crystals in it is terrestrial.
Bubbles. Volcanic rocks or metallic slag on Earth often have bubbles or vesicles in them, but meteorites do not. Vesicular texture ends the enquiry.
A streak. If you scratch a meteorite on an unglazed ceramic surface, it should not leave a streak. This is the one that does the most work, because the minerals most often mistaken for meteorites all streak strongly and distinctively.
So the efficient order is: look for crystals, look for bubbles, then use the streak plate. Three observations, no equipment beyond a piece of unglazed tile, and the great majority of cases are closed before you get to weighing anything.
The streak test in detail, with the three species it disposes of
A streak plate is unglazed porcelain with a hardness of about 6.5 — the unglazed foot of a ceramic tile or mug works perfectly. Drag the rock across it once, firmly, then look at the powder rather than at the mark.
Hematite gives cherry-red to reddish brown whatever the specimen looks like in the hand. Steel-grey metallic hematite, black micaceous hematite and dull red earthy ore all streak the same, which is why hematite is the single commonest false meteorite: it is heavy at a measured density of 5.26 and dark, and it looks convincing until it marks the plate. Our hematite page covers the test at length.
Goethite gives brownish yellow to ocher-yellow, at a density of 4.28. A great deal of what people bring in as meteorites is a goethite or limonite nodule from a gravel pit or a beach. The species is on goethite.
Magnetite gives black, at 5.175, and it is strongly magnetic — which is precisely why it gets mistaken. A magnet sticking hard to a heavy black rock is not evidence of anything except iron. Magnetite is far commoner than meteorites by many orders of magnitude.
Two cautions on the test. An iron meteorite is metal, and metal will smear grey on porcelain rather than leaving a mineral powder; that is a metallic smear, not a streak, and the difference is visible. And a weathered meteorite that has sat in soil for a long time will have oxidised to iron hydroxides on the outside and may well streak brown — so on an otherwise promising specimen, test a fresh surface if one exists.
The positive signs, and how far to trust them
If the disqualifiers have not disposed of the rock, the positive signs are worth working through — but treat them as accumulating evidence rather than as individual proofs.
Density. USGS notes that meteorites are usually quite heavy for their size, since they contain metallic iron and dense minerals. That is real but not decisive on its own: hematite at 5.26 and magnetite at 5.175 are heavy too, and so is baryte at 4.50, which is not magnetic and confuses people for a different reason.
Magnetism. Since most meteorites contain metallic iron, a magnet will often stick to them. Note both hedges — most and often. Lunar and some achondritic meteorites are barely magnetic; magnetite, pyrrhotite and a great deal of industrial waste are strongly magnetic. This test has almost no discriminating power on its own.
Fusion crust. Stony meteorites typically have a thin crust on their surface where it melted. On a fresh fall it is a matte black skin roughly a millimetre thick, sharply bounded against the interior. On anything that has weathered it may be gone entirely. A thick, gradational, rusty coating is weathering, not fusion crust.
Shape. USGS notes that iron-nickel meteorites are rarely rounded, having instead an irregular shape with unusual pits like fingerprints. Those pits, regmaglypts, are genuinely distinctive when present — but a rounded, river-worn or beach-worn cobble is almost never a meteorite.
What none of this replaces is looking at it properly. The identification of a meteorite is ultimately a compositional question — nickel content in the metal, oxygen isotopes, chondrules — and it needs a laboratory or a specialist. USGS says as much: it does not verify meteorites itself, and recommends having specimens examined in person by a state geological survey or a university geology department. In Britain, a university earth sciences department or the Natural History Museum is the equivalent route.
What to do if it survives every test
Rocks do survive all of this occasionally, and then the sensible steps are these.
Stop cleaning it and stop cutting it. A meteorite’s value, scientific and otherwise, depends on its fusion crust and its unaltered interior. Wire-brushing the crust off is the commonest way a genuine find is diminished. The general argument against cleaning is on how to clean mineral specimens and applies here with more force than usual.
Record the find circumstances before you forget them. Where exactly, when, in what — soil, gravel, a ploughed field, a roof. A grid reference and a photograph in situ. For a meteorite this information is not provenance in the collecting sense, it is part of the scientific data, and it cannot be reconstructed afterwards. The recording discipline is the same one on what self-collected means on a label.
Then take it to someone with a laboratory. A university earth sciences department or a natural history museum will look at a genuinely promising specimen, and they will be able to tell you in a few minutes whether it is worth a proper analysis. Good photographs, a scale, and the streak-plate result you already have will get you a much faster answer than the rock arriving in the post with no information.
And if it turns out to be hematite, that is not a wasted afternoon. Hematite, goethite and magnetite are all worth collecting in their own right, and a good botryoidal goethite or a sharp magnetite octahedron is a better specimen than a weathered meteorite fragment. The rest of the collecting guides cover identification more generally, is my rock worth anything is the page for the question underneath this one, and our wanted list is where to tell us what you are hunting for.