Bjurböle

A meteorite that crashed through sea ice in Finland in 1899 and is so crumbly that its chondrules fall out like marbles.

Key facts

Type

Ordinary chondrite (L/LL4)

Fell or found

Fell (witnessed)

Year

1899 (12 March)

Country

Finland

Mass

about 330 kg

Official name

Bjurböle

On the evening of 12 March 1899, a brilliant fireball lit up the sky over southern Finland, followed by thunderous explosions. Near the village of Bjurböle, close to the town of Porvoo on the coast of the Gulf of Finland, a large meteorite crashed through the ice covering the sea and disappeared, leaving a hole several metres across. It was one of the largest meteorites ever to fall in Europe, and it was about to become one of the strangest to recover.

Digging through ice and mud

Local people and scientists organised an effort to retrieve the meteorite from beneath the ice. The water was shallow, but the stone had buried itself in the clay and mud of the sea bed. Workers had to cut through the ice and dig out the mud before they could reach it. When they finally hauled up the meteorite, it broke into many pieces. Altogether, about 330 kilograms of meteorite were recovered.

Crumbly chondrules

Bjurböle is a chondrite, a stony meteorite that never melted and is made largely of chondrules. Chondrules are small rounded grains, usually about a millimetre across, that formed as droplets of molten rock in the cloud of dust and gas around the young Sun. In most chondrites, the chondrules are tightly bound in a fine-grained matrix and are difficult to separate.

Bjurböle is different. It is extremely friable, which means it crumbles easily, and its chondrules can be picked out whole, almost like marbles in a bag. That makes it one of the best meteorites in the world for studying individual chondrules. Scientists have used Bjurböle chondrules to measure their shapes, sizes, chemistry and ages, and to investigate how they formed. Its classification, L/LL4, shows that its chemistry falls between the L (low iron) and LL (low iron, low metal) groups of ordinary chondrites, and that it was only moderately heated in its parent asteroid, so its chondrules remain clear and well defined.

A stone shaped by Earth

Because it fell into the sea and lay in wet mud before being recovered, Bjurböle soaked up water and was affected by its time on Earth. Its crumbly nature may be partly due to its original structure and partly due to the way it was weakened by impact and moisture. Collectors and curators keep Bjurböle in dry, stable conditions to stop it deteriorating further.

Why it matters

Bjurböle is a favourite of scientists who study chondrules, because whole chondrules can be separated from it without cutting or crushing. This has allowed researchers to analyse individual chondrules in ways that would be difficult with more solid meteorites, helping to answer questions about how and when they formed and what the young Solar System was like.

It also shows the determination involved in recovering a meteorite from difficult places. Cutting through sea ice and digging in mud to bring up a stone that then broke apart was no small achievement in 1899. In Finland it remains one of the country's best-known meteorites. Bjurböle is held in Finnish collections, particularly at the University of Helsinki, and in museums around the world.

A note on handling

Because it is so fragile, Bjurböle should be handled with great care, ideally only by trained curators. It is a good reminder that meteorites vary hugely in strength. Some, like iron meteorites, are tough and heavy; others, like Bjurböle, can crumble in your fingers. Never try to break or crush any rock you think might be a meteorite. If you find a suspected meteorite, keep it dry, note where you found it, and contact a museum or university for advice.

Did you know?

See more

Bjurböle in the catalogue