An "amazing" new type of mineral has been discovered by scientists analysing a rock mined in Cornwall about 220 years ago.
The dark green mineral has been named kernowite after Kernow, the Cornish language word for Cornwall.
A group led by Natural History Museum (NHM) mineralogist Mike Rumsey made the discovery while studying a rock taken from Wheal Gorland mine in St Day.
Mr Rumsey said: "It's amazing that in 2020 we are adding a new mineral."
For centuries, mineralogists believed the green crystals to be a variation of another mineral, liroconite, but Mr Rumsey and his team found it has a different chemical composition.
Blue liroconite is highly prized by collectors around the world, and the majority of it comes from the Wheal Gorland site.
Cornwall has a rich mining history with Unesco world heritage status and is known globally for the discovery of minerals.
Mr Rumsey, principal curator of minerals at the NHM in London, said: "A lot of these discoveries happened over 100 years ago when the mines were still active, so the discovery of a new mineral from Cornwall, particularly one that is related to the region's most famous mineral, is really quite amazing.
"Considering how many geologists, prospectors and collectors have scoured the county over the centuries in search of mineral treasure, it's amazing that in 2020 we are adding a new mineral."
Mr Rumsey said most liroconite comes from Wheal Gorland, adding: "The mine was used between around 1790 and 1909, but it has been demolished now.
"There is a housing estate on it and there is nothing left. It's an extinct locality, we can never go back."
"What we've got is a bit like a little time capsule," Mr Rumsey said.
"The fact that this sample was preserved in a museum means that we can do this kind of research because we'd never be able to go back and collect any more."
What is a mineral?
- A mineral is naturally occurring chemical substance formed by geological processes
- A rock is an object formed of one, or many minerals in combination
- Many minerals form beautiful crystals, the most prized being those with bright colours, glass-like transparency and attractive crystal forms
- The gemstone minerals and their varieties, like diamonds, emeralds and rubies have been desirable since ancient times
- The Natural History Museum's mineral collection is one of the most important and comprehensive collections of its type in the world, containing about 185,000 specimens