How do I clean dirt off a meteorite?
Generally, don't clean it, or only gently brush off loose soil. Water, chemicals and wire brushes can damage the crust and cause rust.
It is tempting to scrub a dirty meteorite, but cleaning can do more harm than good.
For fresh falls. Do not clean at all. Scientists want specimens as pristine as possible. Soil and dirt can be identified and removed in the laboratory without destroying information. Washing a fresh fall with water can alter its minerals and contaminate it.
For older finds. If loose soil or sand clings to a specimen, gently brush it off with a soft, dry brush, such as a soft paintbrush or toothbrush. Work over a tray to catch any fragments.
Avoid water where possible. Water encourages rust, especially in iron meteorites and metal-rich stones. If you must use a little water to remove stubborn mud from a stony meteorite, dry it thoroughly and quickly afterwards, for example in a warm, dry place with desiccant. Some collectors use alcohol, such as isopropyl alcohol, because it evaporates quickly, but use it sparingly and with ventilation.
Avoid harsh methods. Never use wire brushes, sandblasting, acids, bleach or abrasive cleaners, which can damage fusion crust and remove scientific information. Heating to dry specimens can cause cracking.
Desert specimens. Desert meteorites may have calcite, caliche or desert varnish coatings. These are part of their terrestrial history and should not be removed by amateurs.
Iron meteorites with rust. Rust removal and stabilisation is specialist work. Seek advice from a museum conservator or experienced dealer.
If in doubt, leave the specimen as it is.