What is the rarest type of meteorite?
Many meteorite types are known from only a handful of specimens, such as some achondrite and carbonaceous groups. Among well-known kinds, Martian, lunar and angrite meteorites are rare.
Rarity can be judged in different ways: by how many separate meteorites of a type are known, or by how much material exists.
The commonest meteorites by far are ordinary chondrites, which make up about four in every five falls. Iron meteorites make up only a few per cent of falls but are common among finds, because they are tough and easy to recognise.
At the other end, some types are known from just a few stones. Ungrouped meteorites, each unlike any other, are by definition unique. Small groups and grouplets, such as the Kakangari chondrites, pyroxene pallasites and Eagle Station pallasites, have only a handful of members. Angrites, among the oldest volcanic rocks known, number only a few dozen, and brachinites and winonaites are scarce too. CI chondrites, the most chemically primitive meteorites, are known from only a handful of falls, including Orgueil, Ivuna, Alais, Tonk and Revelstoke, plus a few finds.
Meteorites from Mars and the Moon are rare in the sense that only a few hundred of each have been named, and many of those are paired fragments of the same fall. Together they make up well under 1 per cent of all named meteorites.
Rarity changes over time. Some types once known from a single stone, such as the R chondrites, became more common as desert and Antarctic searches recovered many new specimens. Discovering new types continues to surprise scientists.