Scientists Found One of the ‘Rarest Minerals on Earth’ Thanks To a Letter Written 75 Years Ago

The members of the geo-team of Bavarian Environment Agency (LfU) Bayern in Germany, Marktredwitz were probably stunned when they found a 75-year-old vintage letter in a drawer of their basement. On this day, they had been tasked with perusing the agency’s extensive mineral and rock collection for geo-archive digitization. While poring through the collection of over 130,000 exhibits, accumulated for over 250 years, one employee stumbled upon this letter, handwritten by a coal miner from 1949.

When Roland Eichhorn, the head of the department, read this letter, something struck him as unusual. The letter mentioned the name of a mineral, humboldtine, that was known to be rare and seldom found in the noted location. But when Eichhorn and his colleagues checked their collection, two cardboard boxes relinquished all their doubts. They reported the “surprise discovery” in a press release.

"We are legally obliged to make geological collection pieces accessible to the public. That is why our geo-archive with holdings from 250 years is currently being digitized. This is when the surprise discovery was made," Eichhorn said in LfU’s press release. In another press release, LfU described that the accidental discovery of this letter was made in February 2023. According to the correspondence from 1949 between Braunkohlenbergbau Maxhütte AG - Zeche Mathias near Schwandorf and the Bavarian Geological State Office (GLA), the coal miner who wrote this letter stated that there was “humboldtine” mineral somewhere in the Mathiaszeche.

According to LfU, humboldtine is a rare organic mineral found only in about 30 locations worldwide including the rhyolite quarries in the Spessart in Bavaria. So, to talk about finding this rare mineral in Mathiaszeche, was something unbelievable. "Skepticism was appropriate. Until now, humboldtine has only been found as tiny crystals in a few places around the world. It was only the in-house laboratory analysis that provided certainty,” Eichhorn said.

Nevertheless, the agency started a search and eventually found the evidence of what was written in the letter, in their Geological Service's rock collection. In one of the drawers cataloged as rare organic minerals, the employees found “two boxes of cm-sized yellowish chunks.” The labels attached indicated that it was indeed humboldtine in these boxes. Further investigation of the crystal’s mineralogical composition using a powder X-ray diffractometer confirmed that it was humboldtine.

Humboldtine’s structure is composed of carbon, water, and iron, which give it its characteristic yellow color. LfU described that there is a brown coal mining site to the northwest of Schwandorf (Upper Palatinate), between Irlbach and Sitzenhof. Mining started on the site in the summer of 1945 but had to be ceased in 1966 due to a massive flood, Forbes says. Brown coal mining was discontinued and the open-pit mine is not recultivated and used as a landfill. So even after coming too close to the source of one of the rarest minerals on Earth, the possibility of actually mining it will forever remain a mystery.

In early 2024, the Munich Show (@the_munich_show) announced that the humboldtine discovered by Eichhorn's team would feature in an exhibit. An avid mineral collector named Andi (@abcmineralien) also posted close-up footage of the yellow humboldtine crystal sitting in a tiny cardboard box. “A rediscovered legendary and once-in-a-lifetime piece,” she wrote on Instagram.