How to identify a meteorite: magnet, crust, streak and common mistakes

Almost every stone people take for a meteorite turns out to be an Earth rock, slag or rusty iron. A few simple tests at home will weed out most mistakes, but only a lab can confirm a meteorite. In Poland, a geology museum or a university can assess a find.

Features to check

Weight. Most meteorites feel clearly heavier than an ordinary stone of the same size, because they contain nickel-iron. Iron meteorites are very heavy.
Magnet. Most meteorites attract a magnet, because they contain metal. Some rare achondrites, such as lunar meteorites, are the exception. Magnetite, a common Earth mineral, also attracts a magnet, so this test only rules things out and confirms nothing.
Fusion crust. During flight through the atmosphere the surface melts and sets into a thin crust. On a fresh fall it is black and matte; with time it rusts and turns brown. Under the crust, on a broken corner, you see a lighter interior.
Regmaglypts. Shallow dents, as if someone had pressed thumbs into clay. They are not pores or bubbles.
Interior. A meteorite is solid, with no bubbles and no layers. On a ground corner of a chondrite you see shiny metal grains and often small, round chondrules.

The streak test

Rub the stone on the unglazed side of a ceramic tile. Most meteorites leave a faint grey or brownish streak, or none. A black streak points to magnetite, and a red-brown one to hematite. Both are Earth minerals and the most common "meteorites" that finders bring in. You can also gently file a small corner. Real metal in a meteorite shines like chrome, not just a dull gleam.

Common lookalikes

Find	How to tell it apart
Furnace slag	Full of bubbles, glassy inside, often with rust streaks. A meteorite has no bubbles.
Magnetite	Attracts a magnet, but leaves a black streak and has no fusion crust.
Hematite	Red-brown streak, often in nodules.
Basalt and other volcanic rocks	Often porous, with bubbles. In Poland usually glacial boulders or road gravel.
Concretions and flints with a black patina	Light, do not react to a magnet, uniform inside.
Rusty iron	Mill balls, shell fragments, machine parts. They lack nickel, which a lab test shows.

A good example of a mistake is the "Kłodawa meteorite". An object brought up in 1986 from a borehole 243 m deep was listed for years as an iron meteorite. Tests in 2007 showed it was steel, probably part of a broken drill bit. It was struck off the meteorite catalogues.

Iron and stony meteorites

Stony meteorites, mostly chondrites, make up most falls. Outside they look like a dark stone with a thin crust, and inside they are grey with specks of metal. Iron meteorites are rarer among falls but found more often, because they resist weathering longer and set off detectors. When cut and etched with acid, many show Widmanstätten patterns, a texture of crossing bands. The pattern only forms when metal cools very slowly, over millions of years, inside an asteroid. A missing pattern does not rule out a meteorite, because some groups do not have it. Stony-iron meteorites, such as Poland's Łowicz, are the rarest.

Safety

If you search with a detector, you may hit unexploded wartime ordnance. Do not pick up metal objects with a regular shape; mark the place and call the police. The same goes for objects that may be archaeological: Polish law says to leave them in place, secure them and notify the regional heritage conservator.

Where to get a find checked in Poland

Take good photos. The whole stone from several sides, the surface close up and, if a corner is broken, the interior. Put a ruler in the frame and give the weight.
Record the place and date. Coordinates from your phone, a photo of the spot, and whether the stone lay on the surface or in the soil. Without this, even a real meteorite loses scientific value.
Write to a museum or university. Meteorites are handled by, among others, the Earth Museum of Adam Mickiewicz University in Poznań, the Earth Museum of the Polish Academy of Sciences in Warsaw, the University of Silesia, which classified the Sołtmany and Drelów meteorites, and the Polish Meteorite Society. Start with an email with photos.
Do not cut or clean the stone. Do not wash it or grind it hard, because you destroy the crust and speed up rusting. Keep it in a dry box.

A meteorite's official name comes from the Meteoritical Society and is published in the Meteoritical Bulletin database. For classification, a sample has to go to a permanent scientific collection, usually about 20 g or 20 percent of a small specimen. A university or institute does the work and then submits the meteorite to the society's nomenclature committee.

For where meteorites have fallen in Poland, see meteorites in Poland, and for the rules, is it legal to search for and sell meteorites.

Sources

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