Carl Axel Arrhenius

Carl Axel Arrhenius (29 March 1757 – 20 November 1824) was a Swedish military officer, amateur geologist, and chemist. He is best known for his discovery of the mineral ytterbite (later called gadolinite) in 1787.

The discovery of ytterbite was the first step in identifying an entire group of previously unknown elements, the rare earths. Eight stable rare earth elements were eventually extracted from ytterbite: terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium.

Early life Arrhenius was born in Stockholm on 29 March 1757 to Jakob Larsson Arrhenius and Brita Sofia Georgii. In 1796 he married Gustafva von Bilang. Returning from Senegal in 1787–1788, Arrhenius met French chemist Antoine Lavoisier during a layover in Paris, France. He became an ardent proponent in Sweden of Lavoisier's new theories of oxygenation and combustion. Lavoisier extensively researched combustion, including that of gunpowder, leading to significant improvements of the quality of this explosive. This advance was of natural interest to Arrhenius. During this visit, in 1787, he found an unusually heavy dark mineral. The mineral's first description was published by Bengt Reinhold Geijer in Crell's Annalen in 1788, where he credited Arrhenius with the discovery of a "Schwerstein" or "heavy rock". Examining a different sample, Anders Gustaf Ekeberg confirmed the existence of a new "earth", calling it "yttria" and the source mineral "ytterbite".

The rare-earths are chemically very similar to each other, almost always occur together in minerals on earth and are rarely found in isolation from other rare-earth elements. Their similarity and co-existence made their initial identification difficult.

The discovery of ytterbite was the first step in a long process of investigations by many scientists in different countries. The identification of new "earths" extended over 100 years, and eventually led to the understanding of elements and their relationships in the periodic system. Ytterbite was eventually found to contain eight stable rare earth elements (terbium , dysprosium , holmium , erbium , thulium , ytterbium , lutetium , and yttrium ). Most of the remaining rare earths were found in the mineral cerite, which contains seven rare earth elements (cerium , lanthanum , praseodymium , neodymium , samarium , europium , and gadolinium ).