Meteorites are classified by the amount of iron they contain, with iron meteorites being the heaviest and most magnetic due to their composition of over 90% iron and nickel. They can come from the core of extraterrestrial planets or even supernovae. Iron meteorites are classified by chemical composition or structure, with 13 standard groups and eight standard structural classes. Famous iron meteorites include Canyon Diablo, Willamette, and Sikhote-Alin.
A meteorite is the name given to the remains of a meteor after it has passed through the earth’s atmosphere and landed on the ground. Virtually all meteorites contain some amount of iron and nickel. Meteorites are classified according to the amount of iron they contain. Iron meteorites contain the most, followed by stony iron meteorites and stone meteorites.
Iron meteorites come from the core of extraterrestrial planets, as opposed to the crust, which yields stone meteorites. Some theories suggest they could even come from supernovae, because iron is produced by nuclear fusion. They are composed of more than 90% of iron, while the remaining percentage consists mainly of nickel. This composition makes an iron meteorite deceptively heavy for its size and highly magnetic. Although they account for about 10 percent of the number of recovered meteorites, their iron makes them account for 90 percent of the mass.
An iron meteorite is classified according to two methods: chemical composition or structure. Classification by chemical composition looks at the amount of trace elements present, anything that is not iron or nickel. These are normally elements like gallium, iridium and germanium. Based on the relative abundance of these, the iron meteorite is placed into one of 13 groups. There is a 14th group of iron meteorites that do not fit into any of the 13 standard groups.
Structural classification is done by examining the two iron-nickel alloys – kamacite and taenite – which are present in all iron meteorites. The iron meteorite is etched with a mild acid which leaves a distinct lattice arrangement of kamacite and taenite known as the Widmanstatten pattern. By measuring the width of the kamacite lines, the structural class is determined. There are eight standard structural classes. There is a ninth for iron meteorites that do not fit into a standard class.
Some famous iron meteorites include Canyon Diablo, which fell in northern Arizona in the United States about 25,000 years ago and was the size of a building. Most of the meteorite was vaporized when it hit the ground, but it left a hole nearly 1 mile (1.6 km) wide and 600 feet (183 meters) deep. The 15-ton (13,600 kg) Willamette iron meteorite was discovered in 1902 in Oregon in the United States and is widely considered one of the most beautiful iron meteorites in the world. Sikhote-Alin fell in 1947 in eastern Siberia, leaving a crater field with 99 distinct impact zones. The Sikhote-Alin fragments have unusually melted as they pass through the earth’s atmosphere, making them highly sought after by collectors.
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