A meteorite is a naturally occurring solid object from interplanetary space that survives impact on a planetary surface. While in space, such an object
is called a meteoroid. The object is called a meteor if it produces light or other visual effects as it passes through a planetary atmosphere.
Most meteorites originate in the asteroid belt, between the orbits of Mars and Jupiter. As asteroids collide they break up into fragments and these
fragments sometimes find their way to earth or other planetary bodies. These fragments and their parent bodies, asteroids, date back to the formation of the solar system,
some 4.5 billion years ago. None of us will likely touch any objects older than these.
There are 3 main types of meteorites: iron, stony and stony-iron. Iron meteorites originate from the asteroid's core, stony meteorites originate from
the asteroid's crust and stony-iron meteorites originate from the asteroid's mantle, the boundary between the crust and the core. Meteorites that are seen to fall are called falls.
Those that are found after the fact are called finds. Meteorites can degrade over time on earth in a process called weathering and many meteorites are subject to rusting
(or oxidation). Most meteorites are attracted to magnets due to the high percentage of iron they contain.
Meteorites are usually named for the location nearest to where they are found such as New Concord, Canyon Diablo or Brenham. Objects
found in areas that don't have specific names, such as items found in Antarctica or the Sahara Desert may be given a general name and a number. For instance a meteorite
found in the Sahara Desert may be designated Northwest Africa 802 or Northwest Africa 869 (the number places it in a class with other meteorites with the same chemical
makeup and the same location. NWA 001 was the first Northwest Africa meteorite found, NWA 002 was the second one found-that wasn't a NWA 001- and so on.)
Often the people who find the meteorites in the desert don't bother having the meteorites checked to see if they match a specific classification and simply sell the meteorites
as Unclassified NWA Meteorites. These items are still meteorites but because they are not specifically classed with a classified meteorite (such as an NWA 802 for example)
they are less valuable. Sometimes the time and expense involved in having a meteorite classified isn't really worth the trouble, especially if the meteorite in question is a small item.
Iron Meteorites compose 5% of meteorites that fall but by far the majority of meteorites that are found and are composed of iron, nickel and other elements. They can be sliced and etched (treated chemically) to reveal Widmanstatten patterns. You would think that the pattern would have been discovered by a man named Widmanstatten, wouldn't you? They were actually discovered by William Thomson in 1804. Thomson published his findings in an obscure Italian journal. In 1808 Count Alois Josep Widmanstatten rediscovered the patterns and they are named after him. Examples of Iron Meteorites are Nantans (China) and Canyon Diablos (Meteor Crater, Arizona).
Nantan (Iron-Nantan County, China)
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