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How to Identify a Meteorite
Perhaps a meteorite has fallen near you, or you have found an odd looking stone and want to know how if you have really found something from outer space.
Here are some pointers to help you learn how to identify a meteorite.
Meteorites arrive in all shapes and sizes, from microscopic dust right through to huge boulders.
Unfortunately, they can also arrive in the size of a small planet, but these events are thankfully very rare indeed.
Several huge meteorites have landed on our planet since its formation 4.5 billion years ago, and each time have effectively wiped out life on Earth as we know it.
The last massive hit took place somewhere in the region of 70 million years ago, and wiped out the dinosaurs.
At the other end of the scale, we have micro-meteorites, space dust, mere particles just a thousandth of a millimetre across.
Scientists tell us that as many as 4 of these micro-meteorites fall per hour, per square kilometre across the Earth's surface, adding up to a massive 40,000 tonnes per annum.
As few as 10 meteorites that are seen to fall, are actually recovered each year. Many fall into the sea and are lost forever.
What are meteorites?
When our solar system first formed, our planets were not on the same equidistant orbit as they are now.
The solar dust left over from the explosions of a previous planetary system swirled around and collided with other, with the bigger fragments joining together until we were finally left with just one sun and several planets.
Huge amounts of rock fragments bombarded the Earth on a daily basis, shaping and resizing our planet.
This continued until about 3.9 billion years ago when things started to settle down.
Gradually, oxygen appeared on the planet and life started.
The dust and small rock fragments that never found a home on one of the planets or moons continues to this day to orbit in a never-ending circle. Scientists can and do track their movements and so can tell us when the next big one is due to pass nearby.
New ones are being created all the time by asteroid collisions on the other planets and moons, which send up new rock fragments into space.
These fragments are called meteoroids when they enter the Earth's atmosphere very high up.
As they are travelling extremely fast, the friction caused by the atmosphere (100 miles up) creates heat, and they start to burn up.
At this point, they can seen from the surface of the planet as a streak of light in the sky. At this point they are known as meteors.
Possibly many thousands of meteors can be seen in the sky every year. The vast majority of them burn up completely and disappear.
Those that pass through to strike the planet's surface are called meteorites.
The very tiny microscopic ones, the micro-meteorites or space dust, do not burn up but pass straight through.
Occasionally larger fragments come through too, and it is those we are now going to focus on.
How to Identify a Meteorite video
Features for Recognizing Meteorites
While there are three broad types of meteorites which you should know about, the vast majority of them are what is known as stone meteorites.
Stone meteorites contain between 5% and 20% of an iron-nickel alloy, and so should be magnetic.
Place a magnet over your 'meteorite' and if it shows no magnetism, then it cannot be a meteorite at all.
90% of all meteorites are stone, the others being made up of iron or stony-iron. The latter two are very magnetic and should be picked up easily with a metal detector.
Blackening of one side
The tremendous heat generated as your meteorite passed through the atmosphere means it will be blackened on one side - the part that was foremost as it passed through.
This is known as fusion crust.
On stone meteorites the fusion crust is much thicker than it is on iron or stony-iron meteorites.
If your meteorite is made of iron, and has been lying on the ground undiscovered for a long time, it may have weathered and rusted, in which case the blackened area will have turned brown.
The presence of chondrules
Chondrules are small lumps of hardened minerals in a stony matrix. They are circular and present all the way through, as would be seen if your stone was cut open.
Planetary stones do not contain chondrules, which are always made up from the silicates of either olivine or pyroxene.
Study photos of chondrules so that you do not confuse them with conglomerate, which can look similar.
Markings known as Widmanstätten pattern are visible on the cut surfaces of many meteorites, especially iron ones.
In summary, you can identify a meteorite by:
- fusion crust
- Widmanstätten pattern
Not all meteorites have chondrules, but the vast majority do.
Iron meteorites are blackened with a very thin fusion crust, and a very misshapen looking exterior.
Stony-iron meteorites are very rare - only 68 have ever been found world-wide, and are among the most beautiful stones ever. These often carry space gems, also known a olivine or peridot.
Have you ever found a meteorite?
If you think you have found a meteorite
Take it along to your local university's geology or astronomy department.
Both will be terribly interested in your rock, especially if it turns out to be a genuine meteorite.
Meteorites are so old they help scientists reconstruct what happened when our solar system was formed.
Stone meteorites are of particular interest, as they are the oldest of all, and many come from failed planets.
Meteorites are worth a fortune, so make sure you do not gift your meteorite unless you are already incredibly rich.
Scientists only need a small part of it to determine its origin and age, through carbon dating and other techniques.
Then you can list your meteorite for sale on eBay or any other online shop, where it will attract the interest of collectors the world over.