uranium dioxide, these two common actinide dioxides can form solid-state solutions and the name of the mineral changes according to the content. Thorite (chiefly thorium silicate, ), also has a high thorium content and is the mineral in which thorium was first discovered. In thorium silicate minerals, the and ions are often replaced with (where M = Sc, Y, or Ln) and phosphate () ions respectively. Because of the great insolubility of thorium dioxide, thorium does not usually spread quickly through the environment when released. The ion is soluble, especially in acidic soils, and in such conditions the thorium concentration can be higher. History Erroneous report In 1815, the Swedish chemist Jöns Jacob Berzelius analysed an unusual sample of gadolinite from a copper mine in Falun, central Sweden. He noted impregnated traces of a white mineral, which he cautiously assumed to be an earth (oxide in modern chemical nomenclature) of an unknown element. Berzelius had already discovered two elements, cerium and selenium, but he had made a public mistake once, announcing a new element, gahnium, that turned out to be zinc oxide. Berzelius privately named the putative element "thorium" in 1817 and its supposed oxide "thorina" after Thor, the Norse god of thunder. In 1824, after more deposits of the same mineral in Vest-Agder, Norway, were discovered, he retracted his findings, as the mineral (later named xenotime) proved to be mostly yttrium orthophosphate. Discovery In 1828, Morten Thrane Esmark found a black mineral on Løvøya island, Telemark county, Norway. He was a Norwegian priest and amateur mineralogist who studied the minerals in Telemark, where he served as vicar. He commonly sent the most interesting specimens, such as this one, to his father, Jens Esmark, a noted mineralogist and professor of mineralogy and geology at the Royal Frederick University in Christiania (today called Oslo). The elder Esmark determined that it was not a known mineral and sent a sample to Berzelius for examination. Berzelius determined that it contained a new element. He published his findings in 1829, having isolated an impure sample by reducing (potassium pentafluorothorate(IV)) with potassium metal. Berzelius reused the name of the previous supposed element discovery and named the source mineral thorite. Berzelius made some initial characterizations of the new metal and its chemical compounds: he correctly determined that the thorium–oxygen mass ratio of thorium oxide was 7.5 (its actual value is close to that, ~7.3), but he