The Rare Earths: Their Occurrence, Chemistry, and Technology

by Stanley Isaac Levy

Gadolinite (Ytterbite).

—Gadolinite is a silicate of iron, beryllium, and the yttria earths, of the formula 2BeO,FeO,Y₂O₃,2SiO₂, which may be written FeBe₂Y₂Si₂O₁₀. According to Groth, it is a basic orthosilicate, Be₂Fe(YO)₂(SiO₄)₂, derived from the acid H₈Si₂O₈. The beryllium content varies considerably, and some authors recognise two varieties of the mineral, one rich, and one poor in beryllium; but Scheerer pointed out in 1840 that iron and beryllium are probably vicarious constituents.

Analysis gives silica 21·8 to 25·3 per cent.; yttria earths 22 to 47 per cent.; ceria earths 5 to 31 per cent. In a variety from Ytterby, the rare earth Scandia was first found, forming up to 0·02 per cent. of the mineral. Small quantities of thoria, ThO₂ may be present, and traces of helium were found by Ramsay, Collie, and Travers. According to Strutt it contains also uranium and radium. Like cerite, it does not often occur crystalline, being usually found in amorphous masses.

The crystals are monoclinic; a : b : c = 0·6273 : 1 : 1·3215; β = 89° 26¹⁄₂´.

Common forms are—Ortho-, clino-, and basal pinakoids, a {100}, b {010}, and c {001}, hemi-prisms m {110}, v {120}, clino-prisms w {012}, q {011}, and many others; and various hemi-pyramids {hkl} and {h̅kl}.

Angles a ∧ m = 32° 6´, c ∧ q = 52° 53´, c ∧ (101) = 64° 9´.

Crystals commonly prismatic, terminated by c. Faces rough and coarse; lustre vitreous to greasy, seen only on freshly-broken surfaces. Brittle. No cleavage. Fracture conchoidal to splintery. Hardness 6¹⁄₂-7; sp. gr. 4·0-4·5.

Colour black, greenish- and brownish-black; green and transparent in flakes. The crystalline variety has strong positive birefringence, with the plane of the optic axes parallel to (b), the plane of symmetry; the amorphous variety is of course isotropic. The brown variety shows very distinct pleochroism, i.e. the colour as seen by transmitted light varies with the direction in which the light traverses the crystal; the green kinds have much weaker pleochroism.

Gadolinite is of common occurrence in the pegmatite veins of the Scandinavian granite. It was first found in a felspar quarry on the island of Ytterby, near Stockholm, by a Lieutenant Arrhenius[24]; it is also found, together with a large number of other rare earth minerals, at Fahlun. It occurs in Norway on the islands of Hitterö and Malö, and in Germany in the Riesengebirge and the Harz. Probably the largest deposit is that in Texas, at Barringer Hill, near Bluffton, on the west bank of the Colorado River, Llano County, now owned and worked by the Nernst Light Company of Pittsburg; in 1904 a mass of very pure gadolinite weighing 200 lb. was found here.[25]

[24] Vide Geijer, Crell’s Chemische Annalen, 1788, 1, 229.