Iron Meteorites

Meteorites are traditionally classified as irons, stones, and stony-irons. The "irons" are composed of nearly pure metallic nickel-iron. This makes it easy to classify them as extraterrestrial in origin because pure metallic iron almost never occurs naturally on the Earth - it is in the form of some oxide. Fraknoi, et al. comment " if you ever come across a chunk of metallic iron, it is sure to be either man-made or a meteorite." The stony meteorites are more common but harder to identify, often requiring isotopic analysis to be sure. The stony-irons, mixtures of metallic iron and stone, are much rarer.

The Casas Grandes meteorite, on display at the Smithsonian Museum of Natural History, has a dimension of perhaps 1.5 meters. It was found in Chihuahua, Mexico. The sliced section here shows it to be essentially solid metal in the interior.

A closer view makes it clear that this is solid metal! There are interesting lines and striations associated with the crystal formation. 更仔细地观察可以清楚地看出，这确实是固体金属！与晶体形成有关的有趣线条和条纹显现出来。

The metal is so solid and so pure that it can be cut into slices! These sections are perhaps a centimeter and a half thick and some 70-80 cm across. 这种金属非常坚固且纯净，可以被切成薄片！这些切片可能有大约一厘米半的厚度，直径约70至80厘米。

Australian Iron Meteorites

This is one piece of a large iron meteorite collection which left 13 impact craters in Australia. It is on display in the Smithsonian Museum of Natural History. It is thought to be about 10,000 years old. This fragment is about a meter across.