Europium.

Chemical composition
Europium metallic EuM-1
Europium metal, grade EvM-1, purity 99.991 %,
TU 48-2-217-72. In bars.
impurities from 0.01-0.08%

  Europium is the most active and one of the most expensive lanthanides. The price of this metal exceeds the price of silver several times and is about 1500 euros per kilogram. But if you search for the word "Europe price," you get a bunch of ads selling this metal at unrealistically high, cosmic prices. Examples can be seen, for example, on the forum bankclub.ru.
One explanation for this phenomenon is an attempt to manipulate VAT refunds by selling europium at highly inflated prices or legalizing illegal income. An example of such fraud is described in the article “Europe is now dear” of the newspaper “New Izvestia”.

Why europium and not thulium, for example, or lutetium, which are more expensive? I don’t know for sure, but perhaps the reason for this is the high activity of Europium. It is oxidized in air faster than calcium, and stored in sealed metal vessels. That is, in theory, the Europeans may not participate in the transaction at all – it is enough to show a sealed vessel and documents, and no one will violate the packaging, under the pretext that Europium will immediately oxidize. In short, there are two European markets. One is real, with prices at a few dollars per gram of europium, and one is fictitious, where they sell europium for several thousand dollars per gram, or try to take loans secured by europium bullion. Something similar is observed with the prices of high-purity copper (99.9999%), Se74 selenium, especially pure mercury (99.9999%) and some other metals.

Currently, europium is used as an activator for the manufacture of yttrium phosphors, as a neutron absorber in nuclear reactors, for the manufacture of laser glasses and crystals.
Europium was discovered by the French chemist Demarce. Interested can download an article on the discovery of Europia (scan, in French)