Should I clean a meteorite?
Usually as little as possible: brush off loose dirt gently, keep it dry, and avoid water, chemicals, scrubbing or grinding, which can destroy the fusion crust and the evidence scientists need; for a possible new find, don't clean it at all.
It is tempting to scrub a muddy rock until it looks its best, but with meteorites the safest cleaning is usually the least. A meteorite's surface records its history: the dark fusion crust formed during its fiery entry, delicate flow lines, and even the weathering it has suffered on the ground. Scrubbing can destroy these features, and water starts rust in the iron metal that most meteorites contain.
If you think you have found a meteorite, don't clean it at all, beyond knocking off loose soil. Place it in a clean paper envelope, aluminium foil or a fresh plastic bag, note exactly where and when you found it, take photographs, and contact a museum or university. Scientists may want to study the outer surface, and fresh falls in particular can carry clues that are easily lost, including organic chemicals in rare types. Any contamination from soap, brushes or skin makes their job harder.
For specimens already in your collection, gentle methods are best. A soft brush, such as a clean paintbrush or toothbrush, can lift dust. A blower of the kind photographers use for camera lenses removes debris without touching the surface. Never use water, bleach, acids, vinegar, rust removers, wire brushes, grinders or sandblasting. These can damage the crust, change the minerals and, in some cases, make the specimen useless to science.
Desert meteorites often have a coating of sand, caliche (a crust of desert minerals) or rust. Removing this is a job for experienced preparers, who use fine tools and patience, and it is often better left alone than done badly. If you are unsure, the golden rule is: do nothing irreversible. A meteorite with honest dirt on it is far more valuable, scientifically and to collectors, than one that has been damaged by enthusiastic cleaning.