Do You Think You May Have Found a Meteorite?

Meteorites are pieces of asteroids and other bodies like the moon and Mars that travel through space and fall to the earth. They are rocks that are similar in many ways to Earth rocks, but it is exciting to find a piece of another planet here on Earth. Meteorites fall to Earth all the time and are distributed over the entire planet, so you could even find one in your own backyard!

When a meteor enters the Earth's atmosphere the resulting fireball produces light, due to the friction between its surface and the air. A smoke or dust trail is produced in the sky by the fireball caused by the removal of material from the surface of the meteorite. Because the fireballs are traveling at high speeds, they sometimes produce a sonic boom or whistling heard 30 miles or more from where the meteorite lands. Several booms may be succeeded by irregular sputtering sounds, comparable to an automobile backfiring.

Meteorites have several distinguishing characteristics that make them different from terrestrial (Earth) rocks. You can use this list to guide you through them. Usually, meteorites have all or most of these characteristics. Sometimes, detailed chemical analyses need to be done, but only on rocks that meet all these characteristics. Since detailed analyses take time and money, look for the easy characteristics first.



Many images on this page are used with the kind permission of Jeff Kuyken, Secretary and Director of the International Meteorite Collectors Association, at www.meteorites.com.au. That site also has a very good page on identifying meteorites.


Meteor-rights!

Fusion crust

Meteorites which have fallen recently may have a black "ash-like" 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 to the right, the fusion crust is the thin, black coating on the outside of the meteorite.

In desert areas, rocks often develop a shiny, black exterior called desert varnish. This develops due to microbial activity on the rock. Usually, but not always, you will be able to see the same kind of varnish on lots of rocks in the same area. This web page has some good examples of desert varnish.


Regmaglypts

The surface of a meteorite is generally very smooth and featureless, but often has shallow depressions and deep cavities resembling clearly visible 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.


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. See more about metal objects below.


Iron meteorites are made of dense and compact metal.

Stony-iron meteorites have metal and olivine crystals.

Metal is distributed evenly throughout ordinary chondrites.

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 man-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.

To measure the density of your rock, you need to measure its weight and its volume. The weight is easy: weigh the rock on a balance or scale (either in grams or in ounces; 1 oz = 28 g). For the volume, get a household liquid measuring cup that is bigger than your rock and fill it halfway with water. Put the rock in and measure how high the water comes now. Subtract the first number from the second number to get the rock's volume. If your rock is too big to put in a measuring cup, then measure it with a ruler (make sure your measurement is in centimeters; 1 in = 2.54 cm). Measure the longest side and the shortest side, then one more length perpendicular to both sides. Calculate a rough volume by multiplying all three lengths together. When you multiply the three lengths together, you will get your answer in cm*cm*cm, or cm3. 1 cm3 = 1 milliliter = 1 mL.

The density is the weight divided by the volume. Compare your rock's density to Earth rocks:

Rock Type
Density in grams / milliliter (mL)
Density in ounces / cup
Granite
2.8
23
Sandstone
2.6
21
Basalt or lava rock
3.1
26
Hematite
5.1
42
Stony meteorite
3.5
29
Iron meteorite
8.0
66


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 man-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.


Chondrules

The most common meteorites to fall on Earth are called chondrites. These are stony meteorites that contain small balls of stony material called chondrules that are about a millimeter (1/25 inch) across. You need to break open the meteorite to see the chondrules.


Meteor-Wrongs

It isn't always easy to identify a meteorite even using the properties discussed above, because some characteristics are shared by common terrestrial rocks and man-made materials. Let's look at some areas where confusion can arise.

Round (Spherical) Shape

Meteorites are almost never perfectly round or spherical and rarely are they aerodynamically shaped. They are usually very irregular in appearance and come in a variety of different shapes and sizes.


Bubbles or holes

Many people believe that meteorites have the appearance of being molten, perhaps having a frothy appearance or bubbles on their surfaces. However, this is not the case. The outer portion of a meteorite, the fusion crust, is either smooth or has the characteristic regmaglypts (thumb prints) described earlier. However, many terrestrial igneous rocks are porous and have holes in them. These holes or 'vesicles' were produced by bubbles of gas that formed in the magma as it was erupted. If you find a rock that is porous or contains vesicles it is a terrestrial rock.

Crystals

If there is quartz (a clear or milky white crystal) it is not a meteorite. Quartz is produced on the earth in evolved rocks at plate margins; in contrast, other planetary bodies like asteroids do not have these kind of settings and do not produce large quartz crystals. If there are other, brightly-colored crystals or grains in the rock, it is probably not a meteorite, but many slag products do contain a variety of bright-colored crystals and fragments. If there is an easily visible crystal structure it might not be a meteorite. This is not conclusive because some of the rarer meteorites do have some crystal structure. However, most ordinary meteorites do not unless viewed under a microscope.

Hot or Radioactive

Most meteorites are cold when they hit the Earth's surface and do not start fires on the ground. Their trip through the atmosphere is short and the friction heat that burns up the outside does not have a chance to heat up the inside of the meteorite.

Meteorites are made of the same elements and minerals as terrestrial rocks and are not any more radioactive than terrestrial rocks, so you can't find them with a Geiger counter.

Streak

Streak is what the rock leaves behind, like a crayon. Common ceramic tile, such as a bathroom or kitchen tile, has a smooth glazed slide and an unfinished dull side which is stuck to the wall when installed. Take the sample that you think is a meteorite and scratch it vigorously on the unglazed side of the tile. If it leaves a black gray streak the sample is almost certainly magnetite, and if it leaves a red-brown streak it is almost certainly hematite. A meteorite, unless it is very heavily weathered, will not leave a streak on the tile. If you don't have a ceramic tile, you can also use the inside of your toilet tank cover (the heavy rectangular lid on top of the tank) - it is heavy, so be careful.

Other kinds of metal

Human activity has produced objects made from pure iron for centuries, so it is possible to confuse lumps of man-made iron with meteoritic materials. Objects such as iron grinding balls often have a smooth rounded appearance and may be thought be meteorites. Lumps of iron slag from smelting processes can also have some similarities to meteorites, so it is important to be careful. The major difference between iron produced by human activity and meteoritic iron is the presence of the element nickel. Iron metal in all meteorites contains at least some nickel whereas man-made metal objects generally do not. In addition, the interior structure of iron meteorites is unique and unlike any man-made metal alloys. Special analysis and preparation techniques are required to examine the internal structure and composition of a suspect meteorite. The results of such tests are, however, completely definitive.


Meteorites in New Mexico

For information on hunting for meteorites in New Mexico, please visit this page.