The quick answer is that although meteorites are very common, they are notoriously difficult to find – unless you are a professional meteorite hunter of course and even then, finds involve a good deal of blood sweat and tears!
People often get excited when they think they have found a meteorite – unsurprisingly! But they are very easy to confuse with other similar-looking rocks, especially lumps of iron ore or industrial slag. So before you allow yourself to get too excited make sure your specimen passes each of these tests!
There are three main types of meteorite, iron meteorite, stony meteorite and stony-iron meteorite which is an ‘intermediate’ between the two other types.
If you can find any Quartz (white mineral) in the stone, then it is definitely not a meteorite, Quartz is produced on Earth so if your specimen has quartz in it it didn’t come from space…..sorry. Some meteorites do have crystals though – for example, stony-iron meteorites often contain visible Olivine (green) crystals.
With only a few exceptions virtually every meteorite is magnetic (due to their exceptionally high iron and nickel content) and so a magnet should be attracted to it. However, just because your specimen is magnetic doesn’t mean that it is definitely a meteorite. Other magnetic rocks are iron ores like Hematite and Limonite, also Magnetite. The magnet test is simple, quick and easy and is a good place to start because if your specimen fails this test then it is almost certainly not a meteorite. Boo hoo – read on..
Anyone who has handled a meteorite, especially big ones, will tell you that they are very heavy. Large pieces of iron ore are also very heavy (noticing a theme here?!). Small meteorite fragments are of course easy to pick up so this is where the concept of density comes in. Density is a measure of how heavy something is in relationship to its size. This allows for accurate comparison despite differences in size. Iron meteorites are incredibly dense and their density is a good way to identify them.
To measure density you need the weight (in grams) and volume (in cm³ or ml) of your specimen. Using scales the weight is simple enough. For a good estimate on volume you can take 3 measurements, the longest side, the shortest side and a side perpendicular (at right angles) to both. Multiply these measurements together to get the volume, and then density is weight ÷volume. An iron meteorite should have a density of 8 (g/ml) or higher and stony iron meteorites have densities of around 3.5 g/ml. Stony-iron meteorites have a density somewhere between these values. If your specimen’s density is 8 or over there is a very strong chance you have a meteorite. However, if your specimen has a density of around 3.5 then whilst it could be a meteorite it could also be a piece of iron ore. Aaha…
Streak is the colour of the mark a mineral leaves when scratched along a ceramic tile. If you don’t have a ceramic tile to hand you can use the bottom of a handy tea mug. Scratch your specimen against unglazed ceramic and observe the colour left behind. If it leaves a red/brown streak your specimen is likely to be Hematite (iron ore), if it leaves a grey/black streak your specimen is likely to be magnetite. A meteorite specimen will not leave any streak, unless it is heavily weathered.
Now for the traits only meteorites have. If you have passed the first four tests try to pass these to be really sure.
Shape and Surface
Meteorites are not especially aerodynamic so a meteorite sample should not be very spherical. The surface should be either smooth and featureless or instead have depressions which look like thumb prints into putty known as regmaglypts .
Chip off a piece of the outer surface of the meteorite. Relatively fresh meteorites will show a ‘fusion crust’, that is, the outside will be different to the interior. This is due to a thin layer of the meteorite melting during its fall through the atmosphere.
On a fresh surface you should often be able to see little flakes of shiny metal; if the interior is plain and uniform then it’s probably not a meteorite. Within meteorites you can also usually find little balls (1mm) of stony material known as chondrules. Chrondrite meteorites are by far the most common type of meteorites to fall on Earth.
If after all these little tests you are still in some doubt you can take your specimen to your local museum for further investigation where they will be happy to give you more help.
For further reference check out these great websites:
And we love to see rocks looking great – that’s why they are so popular with celebrities right now – here’s what to do with your rocks once you have them!!
Good luck with your meteorite finds – if you are getting impatient, check out our site for some we acquired earlier – the early bird catches the meteorite – Happy hunting!