Zagami
A piece of Martian lava that landed close to a Nigerian farmer in 1962 – the largest single Martian stone ever seen to fall.
Key facts
- Type
- Martian meteorite (basaltic shergottite)
- Fell or found
- Fell (witnessed)
- Year
- 1962 (3 October)
- Country
- Nigeria
- Mass
- about 18 kg
- Official name
- Zagami
On 3 October 1962, a farmer was working in his maize field near the village of Zagami, in what was then Katsina Province in northern Nigeria, when he heard a loud explosion. Moments later a stone thudded into the ground just a few metres away from him, burying itself in a hole more than half a metre deep. The stone weighed about 18 kilograms. It was later recognised as a piece of the planet Mars, and it remains the largest single Martian meteorite ever seen to fall.
What is a shergottite?
Scientists divide Martian meteorites into several groups, named after the meteorites that first defined them. Zagami belongs to the shergottites, named after the Shergotty meteorite that fell in India in 1865. Shergottites are the most common type of Martian meteorite. They are igneous rocks, formed when molten rock cooled and crystallised, and most are similar to the basalts and related rocks that make up much of the Martian surface.
Zagami is a basaltic shergottite. It is made mainly of the minerals pyroxene and maskelynite. Maskelynite is not a normal mineral at all. It is a glass made from the mineral plagioclase feldspar, transformed by the enormous pressures of a shock wave without ever fully melting. Its presence shows that Zagami was severely shocked, almost certainly by the impact that blasted it off Mars.
A young volcanic rock
Zagami crystallised from molten rock somewhere on Mars about 180 million years ago, when dinosaurs were roaming Earth. That is extremely young compared with most meteorites, which are about 4.5 billion years old. Such young ages were one of the first clues that shergottites must come from a large planet that remained volcanically active long after small asteroids had cooled.
The rock contains pockets of shock-melted glass. Similar pockets in other shergottites contain trapped gases whose make-up matches the Martian atmosphere measured by spacecraft, a key piece of evidence for their Martian origin. Zagami's oxygen isotopes, the different forms of oxygen in its minerals, also match those of other Martian meteorites.
Zagami is not perfectly uniform, either. Different parts of the stone show slightly different grain sizes and mineral proportions, which record how crystals settled and how the magma changed as it cooled.
From Mars to Nigeria
The impact that launched Zagami into space happened only a few million years ago. The rock then travelled through interplanetary space, gradually exposed to cosmic rays, until its orbit crossed Earth's. Fresh specimens show a black, glassy fusion crust and a grey interior speckled with lighter and darker minerals.
Pieces of Zagami have since reached many museums and research institutions around the world. Because Zagami is relatively large and was available in reasonable quantity, it became one of the most thoroughly studied Martian meteorites. It has been used to investigate how Martian magmas formed and evolved, how much water they contained, and how rocks respond to the extreme shock of being blasted into space.
Why it matters
Witnessed falls are especially valuable to science because the specimens are collected quickly, before rain, soil and air can change them. Of the hundreds of Martian meteorites now known, only a handful were seen to fall, and Zagami is the largest single stone among them. It gives researchers a large, fresh sample of young Martian lava.
Zagami also shows how the study of meteorites has changed. When it fell in 1962, nobody yet knew that rocks from Mars could reach Earth. Within two decades, Zagami and its relatives had become our first physical samples of the Red Planet, decades before any spacecraft could bring one home.
As with all meteorites, it is a reminder that ordinary people who notice something unusual and report it can make a lasting contribution to science.
Did you know?
The Zagami stone landed only a few metres from a farmer working in his field.
It crystallised from Martian lava about 180 million years ago, in the age of the dinosaurs.
Zagami contains maskelynite, a glass formed from feldspar by an enormous shock without fully melting.