Orgueil

A crumbly black meteorite from 1864 whose chemistry is the closest match on Earth to the Sun itself.

Key facts

Type

Carbonaceous chondrite (CI1)

Fell or found

Fell (witnessed)

Year

1864 (14 May)

Country

France

Mass

about 14 kg, in some 20 stones

Official name

Orgueil

On the evening of 14 May 1864, a brilliant fireball lit up the sky over south-western France and broke apart with loud detonations. About 20 stones fell around the village of Orgueil, north of Toulouse. Local people collected them, some still warm. They were unlike most meteorites: soft, very dark, and so crumbly that some could be cut with a knife. Altogether about 14 kilograms were recovered.

A rare and fragile type

Orgueil is a CI carbonaceous chondrite, the rarest and most fragile type of meteorite. The letters CI come from the Ivuna meteorite, which fell in Tanzania in 1938 and gave the group its name. The number 1 means that the rock has been almost completely altered by water inside its parent asteroid. Its original minerals were converted into clays, carbonates, sulphates and tiny grains of magnetite. CI meteorites contain a large amount of water bound up in their minerals, as well as several per cent of carbon, much of it in complex organic compounds. Under the microscope Orgueil also shows tiny magnetite crystals arranged in stacks and raspberry-like clusters, formed as water moved through its parent asteroid.

Because they are so soft and porous, CI meteorites rarely survive long on Earth. Rain and humidity break them down quickly. Only a handful of witnessed CI falls are known, and Orgueil is by far the largest of them.

A match for the Sun

Orgueil's greatest importance lies in its chemistry. When scientists compare the proportions of elements in CI chondrites with those measured in the Sun's outer layers, using the dark lines in sunlight, they find an extraordinary match, except for the most volatile elements such as hydrogen, carbon, nitrogen, oxygen and the noble gases. In other words, apart from these gases, CI meteorites have kept the original mix of elements from which the whole Solar System formed.

For this reason, Orgueil and its relatives are used as the standard for 'Solar System abundances'. Planetary scientists compare other rocks, meteorites and even samples from asteroids with CI composition to work out how they have changed. Samples returned by spacecraft from carbonaceous asteroids have been found to resemble CI chondrites closely.

A 19th-century hoax

In 1964, scientists examining a sealed sample of Orgueil kept since the 19th century made a startling discovery. Some pieces contained seeds and fragments of plant material embedded in the meteorite. Careful study showed that it was a hoax: someone had glued plant material and coal dust into a piece of the meteorite and reshaped it to look natural. The deception may have been linked to the fierce debates of the 1860s about whether life could arise spontaneously from non-living matter. Whatever the motive, it went unnoticed for about a century. It is a reminder that extraordinary claims need careful checking.

Organic chemistry from space

Genuine Orgueil material contains a rich variety of organic compounds, including amino acids, formed by chemical processes on its parent asteroid. Like other carbonaceous chondrites, it shows that some of the raw ingredients of life were made naturally in space and delivered to Earth by meteorites.

Why it matters

Orgueil is a reference rock for the entire Solar System. When scientists talk about the composition of the material from which planets formed, they very often mean the composition of CI chondrites, with Orgueil as the prime example. Its pieces are now held in museums, especially in France, and are handled with great care to preserve their delicate structure.

It is fitting that one of the most important meteorites ever to fall is one of the least impressive to look at: a lump of soft black rock that holds the chemical recipe for the Sun and planets.

Did you know?

See more

Orgueil in the catalogue