Gao-Guenie

A shower of stones over Burkina Faso in 1960 that became one of the most widely distributed meteorites in the world.

Key facts

Type

Ordinary chondrite (H5)

Fell or found

Fell (witnessed)

Year

1960 (5 March)

Country

Burkina Faso

Mass

many stones; total not precisely known

Official name

Gao-Guenie

On the afternoon of 5 March 1960, a fireball broke apart over what was then Upper Volta, now Burkina Faso, in West Africa. A shower of stones fell across the countryside around the villages of Gao and Guénié. People heard explosions, and many stones were picked up. The meteorite was named after the two villages: Gao-Guenie.

A widely shared meteorite

In the decades after the fall, local people continued to find stones in the area, and many specimens reached dealers and collectors around the world. Gao-Guenie became one of the most widely distributed meteorites, especially from the 1990s onwards, when large numbers of pieces were sold. For many collectors and schools, a piece of Gao-Guenie was one of the first meteorites they owned or handled.

That popularity has created a problem. Not all stones sold under the name Gao-Guenie may truly belong to the 1960 fall. Some material sold under the name may come from other finds in the region. Scientists have reported cases of meteorites that were sold as Gao-Guenie but turned out to be different meteorites. This is a reminder that the scientific value of a meteorite depends on accurate records of where and when it was found.

Every officially recognised meteorite is listed in an international database kept by the Meteoritical Society, with its name, type, and where and when it fell or was found. A new meteorite receives a name only after a sample has been studied by a qualified laboratory and the details approved. That system is what allows scientists anywhere in the world to be sure they are studying the same meteorite.

What it is

Gao-Guenie is an H5 ordinary chondrite. Ordinary chondrites are the most common meteorites seen to fall. They are made mainly of the minerals olivine and pyroxene, along with grains of iron-nickel metal and iron sulphide. The 'H' stands for high iron: H chondrites contain the most metal of the ordinary chondrite groups, so they are heavy for their size and attract a magnet. The number 5 means that the rock was strongly heated inside its parent asteroid, blurring the edges of its chondrules, the small rounded grains typical of chondrites.

Many H chondrites are thought to come from a small number of parent asteroids in the inner asteroid belt. Measurements of cosmic-ray effects show that many H chondrites were broken off their parent bodies in collisions over the last few tens of millions of years.

Weathered stones

Because many Gao-Guenie stones were collected long after they fell, they have been affected by the West African climate. Their metal grains have rusted, giving many stones a brown colour inside, and their fusion crusts have often worn away. Freshly collected stones from 1960 look different from those found decades later. Scientists can measure the degree of weathering, which gives clues about how long a meteorite has been on Earth.

Why it matters

Gao-Guenie is important less for any unusual scientific feature than for its role in bringing meteorites to people. Its wide availability has made it a common teaching specimen, allowing students and collectors to see and hold a real piece of an asteroid. It is also a case study in the importance of honest documentation: the value of a meteorite, for science and for collectors, depends on knowing its true origin.

Burkina Faso, like many countries, has laws about the collection and export of meteorites. Anyone buying or selling meteorites should ensure that they come from legitimate sources with proper paperwork. And as always, if you find a suspected meteorite yourself, record where you found it, check the local laws, and contact a museum or university.

Did you know?

See more

Gao-Guenie in the catalogue