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General Information about Meteorites (information from www.meteoritemarket.com)
The following is a test that you can do on the rock that you have found to see if it is likely to be a meteorite.

Meteors enter the Earth's atmosphere at speeds ranging from 14 kilometers/second (31,000 miles per hour) to 45 kilometers per second (100,000 miles per hour). At first they burn on the surface and perhaps explode from the shock. But as they go farther into the atmosphere they slow down. All but the largest meteors (like the one that formed Meteor Crater, located in Arizona) quit burning and fall dark from an altitude of from 5 to 20 km (3.2 to 12.4 miles). That's a long fall. No human can trace the fall of a rock that far. In fact, no human can even see a small rock at that distance. Where meteorites have been observed to fall, there has simply been a whoosh and a thunk.

By the time meteorites hit the earth they are traveling at terminal velocity--that is a velocity at which the resistance of the air will not let them go any faster. They are falling no faster than a rock dropped from an airplane--or the Coke bottle in the first scene "Gods Must Be Crazy." Terminal velocity for a small object is not very high--150 to 300 km/hr (100 to 200 miles per hour more or less) or less. These impacts don't make big craters. You are more likely to see a small indentation in the ground, a small hole, or nothing.

 

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Is the rock magnetic? (information from www.meteoritemarket.com)

About 90% of meteorites will attract a magnet. This is true for iron meteorites and for stone meteorites. You don't need a special magnet--a refrigerator magnet like will do. Here is how to check.

In meteorites almost all of the attraction is the result of native iron. Native iron is iron metal--bright silver-colored when it is cut or sanded. It is malleable--that is it bends rather than breaks. Native iron is extremely rare in natural earth rocks.

Here is how you can expose native iron.
This is a photo of a ground corner. .

 

Not all rocks that attract a magnet are meteorites. A common earth mineral called magnetite will attract a magnet. Here is a photo.

 

Many man-made objects contain native iron. These include slag as well as manufactured objects. If you find a piece of malleable metal that does not attract a magnet, then it is almost certainly a man-made object.

 

Do you still think you might have a meteorite--then on to the next test. Click here.

 

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Some characteristics of meteorites: (information from www.meteoritemarket.com)

Density. Many meteorites are denser than ordinary rocks. An ordinary rock has a specific gravity (this is the measure of density--grams per cubic centimeter) of about 2.5 to 3.0. Most meteorites are made of heavier minerals. The specific gravity can range from 4 to 8. So if you heft a rock and it feels heavy for its size, that is a good indicator. But, be warned, it is not the only indicator. Meteorites can have specific gravities as low as 1.75--less than an ordinary rock.

Chondrules. Most meteorites are chondrites. They have chondrules--spherical grains from 1 to 10 mm (.04" to .4") in diameter. Here are some photos of chondrules.

Thumbprints. A characteristic of the exterior of meteorites is thumbprints--or regmaglypts as scientists would call them.

Rust. Meteorites almost always contain unoxidized iron when land. Once on Earth they begin to rust.

Do you still think you might have a meteorite? . . . then on to the next test. Click here.

 

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Is it shaped like a meteorite? (information from www.meteoritemarket.com)

Most people think that shape is the most important determinant of whether a rock is a Meteorite.

They are wrong. Almost any shape can be a meteorite.

Here are some meteorite shapes:

Meteorites are often squarish.
They can be weird.
They are non-descript--but most often have rounded corners.
They can look like shrapnel.
Some you would never guess.

Here are things that people think are shaped like meteorites, but are not meteorites. These don't bear that much resemblance to the rocks above.

I have never seen a spherical meteorite. This is a moki marble.
Pyrite concretions are probably the rock most commonly mistaken for meteorites.
This is a silica nodule. You can tell by now that I don't like spheres.

 

Now that you know any shape can be a meteorite, you need to go to the next test. Click here.

 

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What is the surface of the rock like? (information from www.meteoritemarket.com)

Does it have Fusion Crust?
Fusion crust is a thin (1 to 2 mm) coating of glass that covers the outside of a freshly fallen meteorite. It is like the glaze on ceramic ware. Usually, fusion crust is black because of iron in the meteorite. But sometimes it is brown or greenish or even clear. It will usually have small cracks and a texture like leather. Iron meteorites and stone meteorites can have fustion crust, but a few--very few--freshly fallen meteorites have none at all.

Meteorites that have been on earth for a while are a different story. The glass coating very often quickly crumbles and falls off.

Here are some examples of fusion crust:

The crust is the black line on the left. The cube is one cm or 0.4 inches
Note the cracks and leather-like appearance.
Note the texture and the left edge where it is broken. Click on photo to see a larger photo.
Note the cracks. Click on photo to see a larger photo.
Click on photo to see a larger photo.
Note the crusted edge. Here a black crust is covered with oxide and mineral. Click on photo to see a larger photo.
Click on photo to see a larger photo.
Here is black crust on a black meteorite. Click on photo to see a larger photo.
Crust on a freshly fallen iron meteorite. Click on photo to see a larger photo.
Shiny black crust covered with mineral mud. Click on photo to see a larger photo.

Here are some meteorites where the fusion crust has weathered:

Weathered crust.
Here the crust is gone.

 

Be warned, some things that look like fusion crust are not fusion crust.

If your rock has fusion crust, that is good news. If not, it is not the end of the line. In either case, you need to go to the next test. Click here.


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Some characteristics that meteorites do not have: (information from www.meteoritemarket.com)

Meteorites almost never have quartz.

Meteorites almost never have bubbles.

Meteorites don't look like river cobbles.

Do you still think you might have a meteorite?--then: Give us a call because we would love to discuss your find with you in person and help you decide what next steps to take if your rock is in fact a meteorite. We can be reached at 608.262.1412, or stop by the museum M-F 8:30am-4:30pm.




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For technical questions or assistance,
please contact museumpa@geology.wisc.edu.