An Accidental Discovery
The story of the Ytterby Mine's contribution to science began with a case of mistaken identity. The mine, located on the Swedish island of Resarö, was originally a quarry for feldspar and quartz, materials used by local porcelain manufacturers. In 1787, a Swedish army lieutenant and amateur chemist named Carl Axel Arrhenius was visiting the quarry when he found an unusually heavy, black rock he did not recognize. Believing it might contain the newly discovered element tungsten, he called it "ytterbite" and sent samples for analysis.
The sample made its way to Johan Gadolin, a chemist at the Royal Academy of Turku in Finland. In 1794, Gadolin published his analysis, concluding that about 38% of the mineral was a previously unknown "earth," or oxide. This new earth was named yttria. The mineral itself was later renamed gadolinite in his honor. This discovery began a century-long process of identifying the many elements hidden within this single type of rock.
Unpacking the Elements
Chemists soon realized that Gadolin's "yttria" was not a single substance but a complex mixture of many similar elements. These rare earth elements are chemically almost identical, which makes separating them extremely difficult. In 1843, Swedish chemist Carl Gustaf Mosander made the next major breakthrough. By carefully experimenting with the yttria, he managed to separate it into three distinct components. One was true yttria, the oxide of the element we now call yttrium (Y). The other two he named erbia and terbia. These would eventually yield the elements erbium (Er) and terbium (Tb).
The work continued for decades. As chemical analysis techniques improved, scientists revisited the minerals from Ytterby. In 1878, Jean Charles Galissard de Marignac isolated yet another element from the mix: ytterbium (Yb). With this discovery, the quarry at Ytterby had given its name, in various forms, to four distinct elements.
Further analysis of the gadolinite from Ytterby led to the discovery of three more elements. Gadolinium (Gd) was named for Johan Gadolin. Holmium (Ho) takes its name from Holmia, the Latin name for Stockholm, the county where the mine is located. Thulium (Tm) is named after Thule, a mythical name for Scandinavia. In total, seven stable rare earth elements can trace their discovery back to the minerals unearthed from this single location.
The mine ceased its feldspar and quartz operations in 1933. The Swedish military then used it for storing jet fuel until 1978. Today, the mine shaft is sealed, and what remains is a small ravine marked by a plaque from ASM International, marking it as a historical landmark.