Was this 'emerald' brought to Earth 108 years ago by the Tunguska meteor? 

It is said that emeralds are the sacred stone of the goddess Venus, yet this translucent specimen may also have an exotic origin. Depending on the light, it appears to be green, or blue, or even orange. The seemingly precious stone was found deep in the taiga on a steep grassy bank of the Metlyakovka River that flows into Kan river, in Krasnoyarsk region.

Lidiya Korshunova, a historian and geologist, said her husband found it after hiking with friends to mark his birthday three and a half decades ago. The men initially believed his find was 'artificial', some kind of glass, linking it, perhaps, to an abandoned mine nearby. This sample - and another he picked up - were used as decorations in the family fish tank.

It was only much later that Lidiya, after reading the papers of Soviet mineralogist and geochemist Vladimir Vernadsky, she began to suspect her aquarium contained something valuable.

She learned that the area her husband found the stone was rich in precious stones. 'Emeralds were found here. And that's when I thought that my stone is precious at the very least,' she said. 

She sought out experts in Moscow: but her hopes were dashed. This was not an emerald. More surprisingly, the scientists could not identify what it was.

Analysis of the 'glass stone' found that compared to ordinary bottle glass it was 7.5 times richer in nickel, 6 times in copper, 20 times in zinc, 3 times in cobalt, 3 times in titanium, and 40 times in chrome. As such, it could not be artificial.

Such quantities of minerals have been found in tektites - some of which are also green. These are glassy objects formed as molten debris in meteorite impacts - and scattered widely through the air.

Renowned Russian scientist, Evgeny Dmitriev, formerly a chief specialist for the Russian Space Agency, suggested that this stone was an orbital travelling companion of the Tunguska meteor which exploded over Siberia on 30 June 1908.

Evidently similar stones - but of a much smaller size - have been found at the epicentre of the Tunguska 'event', which flattened more than 2,000 square kilometres (770 square miles) while causing no known casualties. 

A meteor is believed to have burst some 5 to 10 kilometres above the Earth's surface in what scientists say is the largest 'impact event' on Earth in recorded history, obliterating an estimated 80 million trees. 

The place where the stone is found is some 670 km from the epicentre over Tunguska, also in Krasnoyarsk region. Lidya's stone - now exhibited in the closed town of Zelenogorsk, famous for uranium mining -  where she lives. It is called Kanskit - after the Kan River.