Sunday, January 8, 2012

How to Identify a Meteorite

On one of my trips down state while visiting my friend, Steve, in Mount Pleasant, he had a gathering with some of his friends.   I ended up showing my "wowser" rocks to Matt and Helen Williams.   Matt is a science teacher and wanted to see the rocks. The next day we received a call from the Wiliams.  They wanted to meet with me to show me a rock.

The story about the rock is that several decades ago Helen's grandfather heard a loud noise outside his farm house. When he went out into his yard, there was a newly formed crater around ten feet deep with a small mound at the center.  Steam or smoke was coming out of that mound. They decided to dig in that mound where the found the rock pictured below.  The first shows shows Matt and Helen along with their daughter, Katey, and an exchange student staying with the family, Xlaashi Guo.


Here are some close ups of the rock.




Helen explained that the grandfather never had the rock examined because he was afraid that it would be taken away.  They asked me to verify that it is a meteorite.  I am an agate person and am not familiar with the details of meteorite identification.  So yesterday I decided to do some Internet research.  The best web page I found is:  http://www.aerolite.org/found-a-meteorite.htm.  In fact, from this web page there is an option to pay $10 to have them examine photographs of suspect rocks.  Some of the facts they listed to help identify whether a rock is a meteorite are:

WHAT IS A METEORITE?A meteorite is a piece of iron, stone, or stony-iron composite that has fallen to Earth from outer space. Most meteorites originated within the Asteroid Belt between Mars and Jupiter, and were once part of a planet or large asteroid. A few meteorites come from the Moon and Mars, and a few others may possibly be fragments of cometary material.

Meteorites are valuable both to science and the collecting community. Identification and classification of a new meteorite is a fairly complicated process that can only be handled by a very small number of specialists.



SOME BASIC FACTS
Meteorites are attracted to magnets
Meteorites contain a great deal of extraterrestrial iron, even the ones that look like terrestrial rocks (stony meteorites). Just like a common nail or ball bearing, they will easily stick to a magnet.. Test your find with a good hardware store magnet, or a rare earth magnet .An extremely small percentage of meteorites (far less than one in a thousand) do not show strong attraction to a magnet. They are so rare that we usually discount anything that will not adhere to a magnet. Those meteorites look similar to volcanic rocks from Earth, and are not metallic in appearance.
Meteorites are heavy
Most meteorites are much denser than ordinary Earth rocks. The thing most people say when they hold a meteorite for the first time is, "Wow! It's so heavy!" The unusual weight is due to high iron content. Even stone meteorites will feel heavier in the hand than most Earth rocks.

Meteorites are not radioactive
Meteorites likely traveled in space for millions of years before visiting us here on Earth. They were bathed in cosmic rays, but are not dangerous or radioactive. Some meteorites, such as Canyon Diablo from Arizona, contain micro diamonds but those gems are nearly invisible to the naked eye and can only be seen after cutting a specimen. Meteorites do not contain emeralds, gold (except possibly as a trace element), fossilized aliens, or common earth minerals such as quartz. If your rock looks just like other earth rocks, it probably is one. Meteorites look and feel different from the ordinary rocks around them.

Fusion crust
Recently fallen meteorites will exhibit fusion crust. This is a thin black rind, sometimes shiny, sometimes matte black, which is acquired during burning in the atmosphere. A freshly fallen stone meteorite will look much like a charcoal briquette. Even stone meteorites that have been on the Earth for a long time usually retain some fusion crust and almost always appear much darker than ordinary rocks.

Surface features
Meteorites, especially irons, often acquire "regmaglypts" (thumbprints) caused when their surface melts during flight. Stone meteorites sometimes display regmaglypts too, but they are not as well defined as in irons. Meteorites, particularly irons, may also show angular features such as points and ridges, and also flow lines which are caused by melting. Many of the suspected meteor-wrongs we receive are common terrestrial volcanic rocks. Volcanic rocks (along with other types) often contain small, deep holes, as if they had been repeatedly punctured with a needle. These holes are called vesicles and are caused by gas escaping when lava cools.  Meteorites do not contain vesicles.  Below is a picture from the ID website that shows a rock that is not a meteorite.


NOT A METEORITE
This is a heavy rock which looks metallic but note the small holes caused by escaping gas. Meteorites do not have vesicles

Metallic flakes
Nearly all stone meteorites contain small, bright metallic flakes. These are tiny pieces of extra-terrestrial iron and nickel. You can usually see them after slicing off a small piece, or removing a corner with a bench grinder. Please note! We recommend that you do not cut up your suspected meteorite, or otherwise damage its appearance. A meteorite with a beautiful or interesting shape will be worth less to collectors if its end has been hacked off. Ask a meteorite professional or accredited lab to do your cutting and testing.

Chondrules
Small, colorful, grain-like spheres which occur in most stone meteorites, hence the name of these stone meteorites — chondrites. Chondrites are the most common type of meteorite. Chondrules

Rust or patina
Meteorites which have been on the Earth for a long time will likely start to rust, or — in dry desert environments — acquire a "patina" caused by oxidation. The natural patina of irons is often yellow/ochre, red, or orange.

Temperature of recently fallen meteorite
Despite what we see in Hollywood action movies meteorites are not burning, or even hot when they land upon the Earth. The glowing fireballs we see in the night sky are caused by atmospheric pressure and friction. Meteors stop ablating (burning) approximately seven miles above our planet's surface, then fall in what is known as "dark flight," according to the normal pull of gravity. It is very cold at an altitude of seven miles, so meteorites cool quickly as they plummet towards the Earth. There has never been a documented case of a burning, or even hot, meteorite landing upon the Earth.

So despite the compelling story told by the Williams family, I am not sure if this is a meteorite.  The last paragraph above suggests that meteorites are not hot when they land. If this is true,  then there would not have been steam coming from the bottom of the crater. The web page also says that meteorites never have vesicle hole openings.  You can see from the pictures of the Williams family specimen that it does have vesicles.  But who knows -- maybe this specimen is an unusual rocky meteorite.  It does have some of the "thumbprint" depressions on the surface and does have the orange/red color.  We tried a magnet which didn't seem to stick to the rock, but we didn't use a high quality magnet sot his test was not conclusive. Through my friend, Steve, I sent a link to the meteorite ID website and suggested that they send photos of the specimen in for examination by experts.

I would like to thank the Williams family for sharing their story.  For their sake I hope that the specimen is a meteorite.

1 comment:

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