1. Fusion crust
Meteorites that have fallen recently have a black, glassy or ashy crust on their surface. When a meteorite falls through the Earth's atmosphere a very thin layer on the outer surface melts. This thin crust is called a fusion crust. It is often black and looks like an eggshell coating the rock. However, this crust weathers to a rusty brown color after several years of exposure on the Earth's surface and will eventually disappear altogether. In the image below, the fusion crust is the thin, black coating on the outside of the meteorite.
2. Irregular Shape
The surface of a meteorite is generally very smooth and featureless, but often has shallow depressions and deep cavities resembling thumbprints in wet clay or Play-Doh. Most iron meteorites, like the example at right, have well-developed regmaglypts all over their surface. Ordinary chondrites and stony meteorites like the one at left have smooth surfaces or regmaglypts.
3. Density
Unusual density is one of meteorites' more characteristic features. It's not enough to say your rock is heavy. Density is how heavy a rock is for its size or compared with other rocks. Iron meteorites are 3.5 times as heavy as ordinary Earth rocks of the same size, while stony meteorites are about 1.5 times as heavy. Lumps or fragments of human-made materials, ore rocks, slag (the byproduct of industrial processes) and the iron oxides magnetite and hematite, are also common all throughout the world and are frequently dense and metallic. So this test is helpful but not definitive.
4. Magnetism
Most meteorites contain some iron-nickel metal and attract a magnet easily. You can use an ordinary refrigerator magnet to test this property. A magnet will stick to the meteorite if it contains much metal. Some meteorites, such as stony meteorites, contain only a small amount of metal, but will attract a magnet hanging on a string. Metal detectors can alert you to whether a rock contains metal, but not all metal is magnetic. For instance, aluminum sets off metal detectors but is not magnetic. So, if you find a rock with a metal detector, try the magnet test too. In addition to meteorites containing iron, there are human-made and naturally-occurring materials that are magnetic and are easily confused with meteorites. Magnetite and hematite are common iron-bearing minerals that are often mistaken for meteorites. Both minerals can occur as large masses with smooth surfaces that are heavier than typical rocks, but have some features which resemble meteorites. Magnetite is very magnetic (hence its name) and hematite is mildly magnetic. Use the streak test below to distinguish these minerals.
5. Iron-nickel metal
Most meteorites contain at least some iron metal (actually an alloy of iron and nickel). You can see the metal shining on a broken surface. Meteorites without metal in them are extremely rare and they need to have some of the other characteristics of meteorites to be able to identify them as meteorites. Iron meteorites have a dense, silvery appearing interior with no holes or crystals. Stony iron meteorites are about half metal, half crystals of green or orange olivine. Stony meteorites contain small flecks of metal that are evenly distributed throughout the meteorite. The metal in a meteorite has the unusual characteristic of containing up to 7% nickel. This is a definitive test of a meteorite, but requires a chemical analysis or acid etching to detect.
