Читать книгу The Rare Earths: Their Occurrence, Chemistry, and Technology - Stanley Isaac Levy - Страница 162

[44]—A silicate of yttria earths with water and small quantities of alumina, ferric oxide, carbon dioxide and alkalies. The ratio of rare earths to silica gives the formula R₂O₃,2SiO₂, or R₂Si₂O₇; if the water be included, the formula becomes H₂R₄Si₄O₁₅. The presence of both water and carbon dioxide indicates, however, that the mineral has been somewhat altered, and the simpler formula R₂Si₂O₇, (cf. Thortveitite, below) probably expresses the composition of the original mineral. It contains considerable quantities of nitrogen and helium, though uranium and thorium appear to be absent.

[44] Benedicts, Abstract in Zeitsch. Kryst. Min. 1900, 32, 614.

Monoclinic; a: b: c = 1·154: 1: 0·602. β = 80° 12´.

Common forms are the pinakoids {100} and {010}, hemi-prism {110}, hemi-pyramids {111} and {111̅}, and others, and the hemi-dome {021}.

Angles, (100) ∧ (010) = 91° 0´; (100) ∧ (110) = 48° 9´; (100): (111) = 59° 4´.

Double refraction weak. No cleavage. Brittle. Hardness 6¹⁄₂. Colour, bright flesh-red; translucent, with greasy lustre; sp. gr. 4·227, increasing to 4·29 after ignition. A yellow variety has sp. gr. 4·11-4·16, and is transparent.

The ‘average atomic weight’ of the rare earth metals is 99, from which it appears that these consist chiefly of yttrium, with a smaller quantity of the metals of higher atomic weight.

It was discovered in 1898 by Benedicts, accompanying fluocerite (q.v.) in a quartz quarry at Oesterby in Dalekarlia.