A beige piece of rock roughly oval in shape is on a black background. In the middle of the rock is an opening, revealing dark green crystals hidden within.

The new mineral has been named kernowite, after the Cornish word for Cornwall ©The Trustees of the Natural History Museum, London

Beautiful new emerald-green mineral described from Cornwall

Known from just a single location, a new species of mineral has been described from the UK. 

A sample of rock that was collected from a mine in Cornwall some 220 years ago has turned out to be an entirely new species of mineral.

While most new minerals are so small that their colour isn't easy to appreciate, this latest addition forms large emerald-green crystals.

Mike Rumsey is the Principal Curator of Minerals at the Museum and is the one who initiated the investigation and subsequently discovered the new mineral with colleagues at the NHM and collaborators from Slovakia and the Diamond Lightsource in Harwell, Oxford.

'I was investigating a mineral called liroconite so we could curate it properly, but also because it's my favourite mineral!’ explains Mike. 'Liroconite is this beautiful, gorgeous bright blue mineral that comes from Cornwall and I was trying to understand why its colour varies from bright teal-blue all the way to a dark emerald green.

'It turns out that the darkest green samples are sufficiently chemically different to the blue's that we, as mineralogists, would define it as a new species.'

The new description has now been approved by the governing body and the new species kernowite will be published in Mineralogical Magazine in the new year. A journal started back in the UK in 1876 with founders from the old BM(NH).

New species of minerals

When people talk about the discovery of a new species many will tend to think of a new plant or animal. But when Carl Linnaeus first came up with the now universal system of naming things in the eighteenth century, he also included the minerals within this system.  

This means that whenever a new mineral is described, it is also classed as a new species. 

A close up showing the interior of the new mineral. Dark green crystals can be seen in the hole of a beige coloured rock, on a blackbackground.

Kernowite is distinctive for its large green crystals © The Trustees of the Natural History Museum, London

'Like other branches of natural sciences, minerals and rocks were organised by early scientists in a way that allowed people to recognise connections and links between them,' says Mike. 'The term species in the life sciences really gained traction thanks to the work of Linnaeus.

'He also included the mineral kingdom in his classifications, so minerals ended up with some of the same language for their descriptions. Other terms like genus have not made it through though, as minerals don't really have a strongly hierarchical structure in their organisation, although that's something being discussed by scientists currently.'

To be described as a new species, a new mineral needs to meet a number of criteria.

These relate largely to determining what the chemistry of the new material is and how the atoms within the material are arranged in three-dimensional space and then how that arrangement repeats to make up the crystals that we see. This is what mineralogists call crystal structure.

'In the crystal structure of liroconite, one of the positions where you can put an atom can contain either aluminium or iron,' explains Mike. 'For liroconite, the position is dominantly filled with aluminium and the physical crystal ends up being blue.

'For the new mineral kernowite the position is instead dominantly filled with iron and the result is a green crystal. We think that the more iron the darker the green, but that still needs some more work and more samples to confirm. Both minerals have exactly the same crystal structure meaning that all the atoms are in the same positions, it is just the chemical composition that varies.'

Cornish type

There are only around 100 new species of mineral described every year, and not many with large colourful crystals.

It is even rarer to have a new mineral described from the UK, something which only happens once every three or four years on average. The new species is currently known from a single location in Cornwall, which has given rise to its new name kernowite, after Kernow which is the Cornish word for Cornwall. 

The bright blue shards of the mineral stick up like blades from a creamy-green rock, on a black background.

It has long been thought that liroconite came in a variation of colour from bright blue shown here to deep green. It is now known that the green ones are instead kernowite © The Trustees of the Natural History Museum, London

'Based on it's mining history Cornwall is a world UNESCO heritage site known around the world for the discovery for many new minerals,' says Mike. 'However, a lot of these discoveries happened over 100 years go when the mines were still active, so the discovery of a new mineral from Cornwall, particularly one that related to the regions most famous mineral, is really quite amazing.'

The mine from which kernowite has been found is also the location from which the majority of the world's liroconite is derived, which is highly prized among collectors.

'Most liroconite comes from this place called Wheal Gorland,' explains Mike. '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.'

Because liroconite is such a famous mineral, there could be samples of kernowite in other museums that have for all this time also been grouped with the liroconite, so the community may well discover these now the other curators know what they're looking for.

But with the demolition of the mine, it means that more samples of the mineral may never be found again.

'What we've got is a bit like a little time capsule,' says Mike. '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.'

Hopefully other samples will be found in other public and private collections, but until that happens then the one sample held at the Museum and another in a private collection are the only known examples of Kernowite in the entire world.