Forgotten envelope leads to discovery of rare ‘cyborg’ Earth mineral found in only 8 countries

A forgotten envelope led stunned scientists to uncover one of the Earth's rarest minerals.

From Japan's $26 billion deep-sea discovery to the US' own find on-land, rare Earth minerals have the potential to transform economies if they're found in large enough quantities.

And scientists digitizing their 250-year archive of rock samples in Germany were amazed to find Humboldtine - a mineral so rare, it's only been detected in eight countries.

The geological department at the LfU Bayern had found a 75 year-old letter suggesting the rare Earth mineral was somewhere in their collection.

But it wasn't actually listed in their catalogue, so a search of their 130,000 strong sample collection began.

How much Humboldtine was found?

And amazingly, inside an unsuspecting box were six, hazelnut-sized yellow lumps and a handwritten note which read: "Humboldtine from the Mathias Mine near Schwandorf."

The discovery was initially made in a coal mine (Srinophan69/Getty Images)

The letter is referring to the Matthiaszeche mine - a former open-pit mine for brown coal near Schwandorf.

However, the coal mine closed in 1966, and later flooded - so there's no chance of uncovering anymore rarities from the site.

Incredibly, this tiny stash has doubled the total amount of Humboldtine known in the world so far.

While it's not known exactly how much the mini-haul is worth, collectors claim the mineral can go for 'significant amounts.'

So just imagine how much money a mine-full could bring in...

The discovery stunned scientists (Prögler/LfU)

What makes Humboldtine special?

Roland Eichhorn, head of the geology department, reportedly described Humboldtine as a 'cyborg among minerals.'

At the time, in 2023, he said: "Until now, Humboldtine had only been found as tiny crystals in a few places worldwide."

And while initially there was doubt over the authenticity of the minerals, he confirmed: "Our in-house laboratory analysis provided certainty."

Exactly how they formed in that particular mine, though, left Eichhorn bewildered.

Humboldtine (yellow) seen under a microscope, with halotrichite (white)(Picture: Prögler/LfU)(Progler/LfU)

A history of Humboldtine

Humboldtine is scientifically classified as the iron salt of oxalic acid, otherwise known as FeC₂O₄·2H₂O.

It forms under very specific conditions where iron-rich rocks interact with organic acids in damp environments, such as lignite (brown coal) deposits.

The mineral was first discovered by German mineralogist August Breithaupt in 1821, in a weathered brown coal deposit in the Czech Republic.

It's only been found at 30 sites across just eight countries since; the US, the UK, Canada, Brazil, Germany, Italy and Hungary.

Its unique composition giving it a distinctive yellow color.

In synthetic form (iron(II) oxalate), it can be used in battery materials research and 'green' chemistry as a precursor for iron-based electrode compounds.