Imilac

A pallasite scattered across the Atacama Desert, whose weathered pieces look like metal sponges.

Key facts

Type

Stony-iron, pallasite (main group)

Fell or found

Found

Year

1822 (first reported)

Country

Chile

Mass

hundreds of kilograms in many fragments

Official name

Imilac

The Atacama Desert in northern Chile is one of the driest places on Earth. Some parts receive almost no rain for years at a time. These harsh conditions make it an excellent place for meteorites to survive, and one of the most famous finds from the region is the pallasite called Imilac, named after a locality in the high desert east of the port of Antofagasta.

Discovery and dispersal

Imilac was reported to the outside world in the 1820s. Over the following decades, travellers, miners and collectors picked up many fragments, and specimens were sent to museums in Europe and elsewhere. The meteorite fell as a shower of fragments scattered over a strewn field, and searchers have found pieces of many sizes. In total, hundreds of kilograms have been recovered.

A sponge of metal

Imilac is a pallasite, a stony-iron meteorite made of crystals of the mineral olivine set in iron-nickel metal. Pallasites are among the most beautiful of all meteorites, especially when cut, polished and lit from behind.

What makes many Imilac specimens distinctive is their weathering. In fragments that lay exposed on the desert surface, many of the olivine crystals have been loosened and removed over time, leaving behind a skeleton of metal full of holes. The result looks like a metal sponge or honeycomb, with empty pockets where crystals once sat. Other pieces, especially those that were protected, still hold their olivine, which can be yellowish-green or orange-brown.

Where olivine survives, weathering often changes its colour: fresh olivine is usually greenish yellow, but as the iron in it slowly oxidises it can turn brown or orange. These weathered fragments make Imilac very recognisable and show how even metal-rich meteorites change over thousands of years on Earth.

Where pallasites come from

Scientists have long thought that pallasites formed at the boundary between the metal core and the rocky mantle of a melted asteroid, where olivine and liquid metal mixed. More recent studies have proposed other ideas, such as collisions that injected molten metal into the olivine-rich mantle of another body. Imilac belongs to the main group of pallasites, which share similar chemistry and are thought to come from closely related sources.

Scientists have also used pallasites, including Imilac, to study ancient magnetic fields. Tiny metal grains inside some pallasites recorded the magnetic field of their parent body as they cooled. These records suggest that the parent body had a churning liquid core that generated a magnetic field, as Earth's core does today.

A desert treasure

The Imilac area lies high on the Atacama plateau, a long way from any town. The Atacama has yielded many meteorites, as researchers and hunters have searched its stony plains. Imilac is one of the best-known finds there. Like Vaca Muerta, another famous Chilean meteorite, it reflects the region's long history of mining and exploration.

Chile has laws that regulate the collection and export of meteorites, and some sites are protected. Anyone exploring the desert should follow local rules and take great care, as the Atacama can be dangerously dry and remote.

Why it matters

Imilac is a classic pallasite, represented in many museum collections around the world. Its weathered 'sponge' specimens show what happens to pallasites in desert conditions, and its better-preserved pieces offer fine examples of olivine in metal. Studies of pallasites like Imilac help scientists understand how early asteroids melted and separated into layers, and whether they generated magnetic fields like Earth.

If you see a piece of Imilac in a museum, look closely at the holes in the metal. Each one marks the place where a crystal of olivine once formed, deep inside a long-vanished world.

Did you know?

See more

Imilac in the catalogue