How Do You Know if You Found a Meteorite?
Ultimately the answer to this question will probably be answered by a testing laboratory associated with a museum or
university. However, if you have ever had the experience of sending a sample in for testing, as I have, you know that the process can be lengthy and frustrating. Typically there is a backlog of samples to be tested and in most cases universities
do not have an abundance of funds allocated for this purpose,
so it will require some patience on your part and a willingness to donate a portion of your find to the institution,
should it turn out to be a meteorite. This is to help compensate them for their time, efforts and the expenses associated with testing. Not a bad deal by any means, it is just not a speedy process.
However, there are several simple tests that you can follow that will go a long way towards identifying whether or not you have found a meteorite.
1,) First, is your sample magnetic. Almost all meteorites have some iron, usually in alloy with nickel, and will be attracted to a magnet. If your specimen is not magnetic, there is about a 98% chance it is not a meteorite. Even if it is magnetic that is not a guarantee that it is a meteorite. There are some terrestial rocks that are naturally magnetic such as magnitite and hematite. These two examples can easily be tested for by using a streak test. That is take a ceramic tile, the rough porous side, and scratch it with your sample. If it leaves a black or dark grey streak it is probably magnitite, if it leaves a redish brown streak, it is most likely hematite. Also,
keep in mind there are some man made rocks such as foundry slag what will also pass the magnet test that you need to be aware of.
2.) Second, does your sample rock have what appears to be a fusion crust? As a meteorites passes through the earth's atmosphere it becomes very hot and this will discolor the exterior of the meteorite. If your rock appears different from other rocks in the immediate vacinity and has a black smooth
exterior or in many case redish or dark brown (do to oxidation) it is worth examining further. This fusion crust , when examined in cross section, will normally appear to be very thin, similar in thickness to the skin of an apple.
Magnetic sticking to surface..
3.) Third, does your sample seem heavier that other rocks? The average density of terrestial rock is around 2.7 grams per cubic centimeter The average density of a meteorite, depending of course of the iron nickel content can vary from 3.5 to 8.0 grams per cubic centimeter. The density of iron is 8 grams per cubic centimeter. Almost all meteorites will seem heavier than normal for there size.
4.) Does your sample contain chondrules? The most common meteorites that fall to earth are stony meteorites called chondrites. They get their name from small stony balls tipically about one millimeter thick (1/25th of an inch) in the matrix.
5.) Fifth, if your sample contains quartz, it is propably not a
meteorite. To my knowledge quartz has never been found in a meteorite. The same can be said for fossils. With the exception of one very isolated example, fossil do not occur in meteorites. Fossil, on the other hand are very common in terrestial rocks. And one last point. Where did you find your
specimen? If you found it in a know meteorites spew field, your chance are significantly improved. On the other hand if you found it several hundred yard from a metal foundry, well, good luck.
If all else fails, here is a list of laboratories that can help you get a positive ID.
National Museum of Natural History
Department of Mineral Sciences
Washington, D.C. 20560
Center of Meteorite Studies
Arizona State University
Tempe, AZ 85721
Institute of Geophysics and Planetary Sciences
University of California at Los Angeles
Los Angeles, CA 90024
Note the white chondrule
in the center of this specimen.