Meteorites and Their Properties

VI. The Appearance of a Freshly-Fallen Meteorite

The most important primitive meteorites are generally those that were observed falling and collected soon after hitting the ground. These samples are particularly useful because they have not been altered by chemical and physical processes (such as rain) that are typical of the Earth's surface.

Freshly-fallen meteorites are usually the easiest to identify, because they are surrounded by a fusion crust produced when the surface of the meteoroid was melted by friction with the Earth's atmosphere. (You may recall that when space capsules or shuttles return to Earth, they are protected by heat shields to prevent the spacecraft from being consumed.). Fusion crusts are usually black or brown. Sometimes they contain flow lines radiating from one end of the meteorite towards the other, indicating the thin skin of melt was being "blown" backwards. These samples are called oriented meteorites, because we can tell how they were oriented when they fell through the atmosphere.

If a sample is unbroken and has a complete fusion crust, handle the sample gently to preserve the fusion crust. To see the interior of the object, only chip away or grind off a very small portion of the sample. If the interior resembles one of the meteorites described above, bring the sample to a credible laboratory where a complete examination can be properly documented and precautions can be taken to preserve the integrity of the sample.

If you believe you have found a freshly-fallen meteorite, try to photograph the area before removing any specimens. If a meteorite has produced a crater, measure its diameter and depth (some may only be a few centimeters deep). You should also look for multiple meteorite fragments scattered around the area. If you find more than one, try to estimate the distance between the samples.

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