Fukang

A tonne-sized pallasite from the mountains of north-west China, packed with gem-like crystals.

Key facts

Type

Stony-iron, pallasite (main group)

Fell or found

Found

Year

2000

Country

China (Xinjiang)

Mass

about 1 tonne (main mass just over 1,000 kg)

Official name

Fukang

In 2000, a large, rusty-looking rock was found in mountainous country near the city of Fukang, in the Xinjiang region of north-west China. It weighed just over a tonne. It did not look especially remarkable from the outside. But when a slice was cut from it and polished, it revealed a dazzling interior of large golden-green crystals set in shining metal. Fukang turned out to be one of the largest and most beautiful pallasites ever discovered.

A rare kind of meteorite

Pallasites are stony-iron meteorites, made of roughly equal amounts of metal and stone. The metal is an iron-nickel alloy, and the stone is mostly olivine, a magnesium-iron silicate mineral that is also common in Earth's mantle. When the olivine is clear and gem-quality, it is called peridot. Pallasites make up only a small fraction of all known meteorites, so a single mass of more than a tonne is an exceptional find.

Fukang belongs to the main group of pallasites, which share very similar chemistry and are thought to come from the same parent body, or a few closely related ones. Its olivine crystals are large, often several centimetres across, and many are angular, broken fragments rather than smooth rounded grains.

How did it form?

The classic idea is that pallasites formed at the boundary between the molten metal core and the rocky mantle of an early asteroid, where olivine crystals and liquid metal mixed together and then cooled very slowly. Some recent research has suggested alternative scenarios, such as collisions between bodies that drove molten metal from one into the olivine-rich mantle of another. Angular olivine fragments like those in Fukang have been used as evidence that some pallasites formed in violent, rapid events in which crystals were broken and mixed with metal before everything cooled.

Whatever the details, pallasites tell us that some asteroids in the early Solar System grew large and hot enough to melt and separate into a metal core and a rocky mantle, much as Earth did.

A star of the show

The Fukang meteorite gained international attention when it was displayed at a major gem and mineral show in Tucson, Arizona, in 2005, where visitors marvelled at polished slabs glowing with light. It later appeared at auction and in exhibitions, and slices were distributed to collections and researchers. Much of its material was cut, so that the olivine could be seen and studied, but the remaining main mass is still very large.

Cutting a pallasite is a tricky job. The hard metal and the fragile crystals respond differently to saws and polishing, and the olivine can easily crack or fall out. Specialists use careful techniques, and stabilisers, to keep slices intact. That is professional work, not something to try at home.

Why it matters

Fukang offers scientists and the public a remarkable window into the interior of a small planetary body. Its size means that there is plenty of material for study, including how olivine crystals were broken and rounded, how the metal crystallised, and how fast the whole mass cooled. Researchers can measure the chemistry of its olivine and compare it with other pallasites to test ideas about where and how they formed.

It also shows how meteorites often reach science through many hands: a finder, dealers and collectors, and finally museums and researchers. Throughout that chain, accurate records of where and when a meteorite was found are essential, and local laws about collecting and export must always be respected.

When you look at a slice of Fukang held up to a window, the colours you see come from crystals that formed in a world that was torn apart long before Earth's oldest surviving rocks were made.

Did you know?

See more

Fukang in the catalogue