[1] Chalcopyrite, or Copper pyrites, is a mixed sulphide of iron and copper, of the approximate formula CuFeS₂.
[2] For the history of the name Tungsten, see under the mineral [Cerite], [Ch. II].
[3] The history of these names will be found somewhat more fully under [Gadolinite], [Ch. II].
During the nineteenth century a considerable number of rare earth minerals was discovered and analysed; the quantities of the minerals observed, however, were so small that the name ‘Rare earths,’ applied to the new oxides found, was in every sense justified. Until the year 1885, though by that time the scientific interest of the group had been fully demonstrated by the discovery of several new elements, it was supposed that the minerals were almost entirely confined to a few scattered localities in Scandinavia and the Ural mountains. In that year Dr. Auer von Welsbach announced his application of the rare earths to the manufacture of incandescent mantles. Immediately there was a great demand for raw material for the preparation of thoria and ceria. The agents of the Welsbach Company visited all the important mining centres of Europe and America, intent on a search which shortly made it clear that the metals of the so-called ‘rare earths’ are really quite widely distributed in nature. The chief commercial deposits are the monazite sands of the Carolinas, the Idaho basin, and Brazil, the gem-gravels of Ceylon, and the remarkable deposits of gadolinite and allied minerals at Barringer Hill in Texas.
Whilst deposits of commercial importance are not very common, improved scientific methods and more careful search have shown that in traces the rare earths are of exceedingly wide distribution. Sir William Crookes has shown that yttria earths are often present in calcite and in coral; whilst Headden[4] noted that quite considerable amounts (up to 0·03 per cent.) were present in a yellow phosphorescent variety of calcite from Colorado. Similarly Humphreys[5] found that fluorspar usually contains traces of yttrium, whilst one or two phosphorescent varieties contain quantities varying up to 0·05 per cent. The presence of yttria elements in phosphorescent varieties of calcite is interesting, and some connection has been suggested; there is, however, no positive ground for the belief in such a relation.
[4] Amer. J. Sci., 1906, [iv.], 21, 301.
[5] Astrophys. J., 1904, 20, 266.
More recently Eberhard[6] has found very considerable quantities of rare earths in cassiterite (tin dioxide, SnO₂) and wolframite [an iron manganese tungstate, (Fe,Mn)WO₄]. A specimen of wolframite from the Erzgebirge was found to contain nearly 0·4 per cent. of rare earths, over half of this quantity being scandium oxide. A process which is readily susceptible of commercial application has been worked out by R. J. Meyer,[7] for the extraction of scandia and the yttria earths from the mixed oxides left after the treatment of wolframite for tungstic acid.
[6] Sitzungsber. königl. Akad. Wiss. Berlin, 1908, 851; 1910, 404.
[7] Meyer, Zeitsch. anorg. Chem., 1908, 60, 134. Meyer und Winter, ibid., 1910, 67, 398.