Pupils at a school in Austria were evacuated because a rock they had on display was giving off radiation.
The rock turned out to be a lump of uranium, the metallic element that is used to produce atomic bombs.
Alarmingly, the uranium was giving off thousands of millisiverts of radiation into the Missionaries of the Sacred Heart School in Salzburg - a lot higher than what is given off naturally.
Fortunately the rock was identified when anti-nuclear campaigner Thomas Neff came into the science lab to give a talk.
Danger: The rock was removed from the classroom and placed in storage (Salzburg.gv.at)
During an experiment with a watch containing radium, Neff began to measure levels of radiation in the room using a Geiger counter - and realised there was 20 TIMES the typical amount in the room.
And it was when he approached the rocks that the reading went through the roof, shooting up to 102,000 counts per minute - far higher than the 60 counts expected in a normal reading.
Neff alerted the school and pupils were evacuated while the rock was recovered and placed into storage.
Following the discovery, more schools in Salzburg were found to have uranium lumps on display and they were all removed.
A radiological laboratory in Austria said: “The radioactive screening and the risk assessment show a basic risk potential in Salzburg schools in case of improper storage.”
Top pic: Rex