It was stated above that zirconium was found in euxenite in 1879. In 1901 Hofmann and Prandtl[72] declared that zirconia was an unfailing constituent of the mineral, and that it was always accompanied by a new oxide, which they named Euxenia (‘Euxenerde’). This was characterised by the solubility of its oxalate in acid solutions, the insolubility of the precipitated hydroxide in excess of alkali, and the gradual precipitation by hydrogen peroxide from a slightly acid solution of its salts. In their paper quoted above, Hauser and Wirth state that zirconia is never present in typical euxenites. In a second paper[73] they state that after exhaustive treatment of every known zirconia mineral, they can find no trace whatever of the ‘new earth,’ and conclude that Hofmann and Prandtl must have made some experimental error. During this examination, they observed radioactivity in some minerals which contained no traces of uranium or thorium.
[72] Ibid. 1901, 34, 1064.
[73] Ber. 1910, 43, 1807.
Risörite.
[74]—A columbate of yttria earths, with titanium; ferric oxide, alumina, lime and lead monoxide are present in small quantities. It resembles fergusonite in composition, but differs in the almost complete absence of uranium, the high loss on ignition, and the amount of titanium present, which is here considerable (TiO₂ = 6·5 per cent.). Hauser regards it as an orthocolumbate, R´´´(Cb,Ta)O₄, with an isomorphous admixture of metatitanate, R´´´₂(TiO₃)₃.
[74] Hauser, Ber. 1907, 40, 3118; Zeitsch. anorg. Chem. 1908, 60, 230.
The rare earths are chiefly yttria, with some erbia earths and a little terbia; ceria, lanthana and didymia are also present. The mineral contains a considerable amount of helium, which is remarkable in view of the very small content of uranium and thorium (cf. [Thalenite]). It is radioactive, the active constituent being precipitated with the lead (and to a very small extent with the rare earths).
It is infusible, but at a red heat it loses much water, and becomes very brittle, with increase of specific gravity; no glowing is observed. It is attacked by boiling concentrated sulphuric acid, and by fused potassium bisulphate; also by hydrofluoric acid (40 per cent.), with separation of the insoluble rare earth fluorides.
No good crystals have been found, and no crystallographic data are known; examined by polarised light it appears isotropic, but this may be due to alteration. Colour, yellowish- to greenish-brown. Streak, yellowish-white. Hardness 51⁄2; sp. gr. 4·179, increasing to 4·678 after ignition (cf. [p. 38]).
The mineral was found in a granite-pegmatite at Risör, South Norway.