Stannern
A shower of basaltic stones that fell on Moravia in 1808 and gave its name to a distinctive kind of lava from Vesta.
Key facts
- Type
- Achondrite (eucrite, HED group)
- Fell or found
- Fell (witnessed)
- Year
- 1808 (22 May)
- Country
- Czech Republic
- Mass
- about 50 kg, in hundreds of stones
- Official name
- Stannern
Early on the morning of 22 May 1808, people near the village of Stannern, now known as Stonařov, in Moravia, in today's Czech Republic, heard loud explosions. A shower of stones fell over the fields and surrounding countryside. Hundreds were collected, together weighing roughly 50 kilograms. Most were small, and many had shiny black crusts. The fall happened only five years after the famous shower at L'Aigle in France had convinced scientists that stones really do fall from the sky. Stannern was investigated promptly. Karl von Schreibers, who was in charge of the imperial natural history collections in Vienna, gathered witness accounts and stones, and his work helped make Vienna one of the great early centres of meteorite study. Many Stannern stones are still held there.
A meteorite like lava
Stannern is a eucrite, a type of achondrite. Achondrites are stony meteorites that do not contain chondrules, the small round grains found in most stony meteorites, because they formed from melted rock. Eucrites are basalts, rocks formed from lava or shallow magma, made mainly of the minerals pyroxene and plagioclase feldspar. On Earth, similar rocks form in volcanic areas such as Iceland and Hawaii.
The name 'eucrite' comes from a Greek word meaning 'easily distinguished', because their minerals are easy to tell apart.
Fresh Stannern stones have a glossy black fusion crust. Eucrites often have especially shiny crusts, because their composition melts into a smooth glass when heated during the fall through the atmosphere.
The Stannern trend
Eucrites are not all identical. Some contain more of certain elements than others. Stannern is richer in what geochemists call incompatible elements, such as titanium and the rare earth elements. These elements tend to stay in the liquid when magma crystallises, rather than fitting into the crystals. As a result, they become concentrated in the last liquids or in melts formed in particular ways.
Eucrites with this kind of composition are described as following the Stannern trend, named after this meteorite. Stannern itself is the type example, the reference against which others are compared, so its name appears in scientific papers about eucrites to this day. Scientists have proposed that Stannern-trend eucrites formed when ordinary basaltic magmas mixed with partial melts of the existing crust, picking up extra incompatible elements. Studying them helps researchers understand how magma behaved on their parent body, and the origin of Stannern-trend eucrites remains an active area of research.
From Vesta
Eucrites belong to the HED family of meteorites, together with howardites and diogenites. They are thought to come from the asteroid Vesta, one of the largest bodies in the asteroid belt. Vesta melted early in Solar System history, forming a metal core, a rocky mantle and a basaltic crust. Eucrites like Stannern are pieces of that crust. NASA's Dawn spacecraft, which orbited Vesta in 2011 and 2012, found surface compositions consistent with the HED meteorites.
Why it matters
Stannern is one of the classic eucrite falls, studied for more than two centuries. It gave its name to an important chemical trend that helps scientists understand volcanic processes on another world. Its many stones were widely distributed, so specimens are held in museums across Europe and beyond.
It also connects to a key moment in the history of science. Coming soon after scientists accepted that meteorites fall from the sky, it helped build up the early collections that allowed them to compare different meteorites and recognise distinct types.
When you see a small black-crusted Stannern stone, remember that it is a fragment of volcanic rock from the crust of an asteroid more than 500 kilometres across, which fell on a Moravian village more than 200 years ago.
Did you know?
Stannern fell only five years after the L'Aigle shower convinced scientists that stones fall from the sky.
The 'Stannern trend' is a chemical pattern in eucrites named after this meteorite.
The name eucrite comes from a Greek word meaning 'easily distinguished'.