Holbrook

In 1912 thousands of stones rained down near a railway station in the Arizona desert – and people are still finding them.

Key facts

Type

Ordinary chondrite (L/LL6)

Fell or found

Fell (witnessed)

Year

1912 (19 July)

Country

United States (Arizona)

Mass

about 220 kg, in some 14,000 stones

Official name

Holbrook

On the evening of 19 July 1912, people near the small railway station of Aztec, a few kilometres east of the town of Holbrook in Arizona, heard a series of loud explosions. A fireball broke apart in the sky, and a shower of stones clattered down over the dry desert. They ranged from pea-sized fragments to stones weighing several kilograms. The Holbrook meteorite shower had arrived, and it would become one of the most famous in North America.

A desert littered with stones

The stones fell over an elongated area several kilometres long. Local people, railway workers and visiting scientists began collecting them, and in the following months and years many thousands were picked up. An estimate often quoted is around 14,000 stones, with a total mass of about 220 kilograms. Most of them were small, many weighing only a gram or so. Because the stones are so numerous, Holbrook specimens are often used in schools and museums to show how a single fireball can deliver thousands of meteorites.

The flat, open desert around Holbrook was an excellent place for a meteorite shower, because the dark stones with their black fusion crusts stood out against the pale ground. Even so, many small pieces were missed. Over the following century, rain and wind have gradually exposed more stones, and meteorite hunters have continued to find Holbrook specimens long after the fall.

What it is

Holbrook is an L/LL6 ordinary chondrite. Ordinary chondrites are the most common meteorites seen to fall. They are made mainly of the minerals olivine and pyroxene, with small grains of iron-nickel metal and iron sulphide. 'L/LL' means its chemistry falls between the L (low iron) and LL (low iron, low metal) groups, so it contains less metal than H chondrites. The number 6 tells us the rock was strongly heated inside its parent asteroid, so its chondrules, the tiny rounded grains that are typical of chondrites, are partly blurred and recrystallised.

Weathering in the desert

Holbrook offers scientists an unusual natural experiment. Stones collected immediately after the fall are fresh and unaltered, while stones found decades later have spent many years exposed to desert conditions. By comparing them, researchers can see how meteorites weather on Earth: how the metal grains rust, how the fusion crust changes, and how minerals from the soil, such as carbonates, gradually seep into cracks. This helps scientists estimate how long other desert meteorites, which were not seen to fall, have been lying on Earth's surface.

A hunter's favourite

Because the strewn field is relatively well known and stones are still found, Holbrook has become a classic training ground for meteorite hunters. Searchers walk slowly across the desert in lines, scanning for small black stones, and some use metal detectors to find pieces rich in metal. Much of the land is privately owned or managed by public bodies, so permission and local rules always come first. Some areas are off-limits to collecting.

The nearby Petrified Forest National Park is famous for fossil wood. Collecting anything there, including rocks and wood, is not allowed, a reminder that every site has its own rules.

Why it matters

Holbrook is one of the best-documented meteorite showers of the early 20th century. It has supplied museums around the world with specimens of a common meteorite type, and it has helped scientists understand how meteoroids break up in the atmosphere and how meteorites weather afterwards. It also shows that a meteorite fall is not a single moment: its stones can go on being discovered for generations.

So if you ever see a tiny Holbrook stone in a collection, it might have been picked up in 1912 or decades later. Either way, it fell from the same fireball on the same summer evening.

Did you know?

See more

Holbrook in the catalogue