It is found only massive or granular. Colour usually white to violet-blue, sometimes reddish-brown. Hardness 41⁄2; sp. gr. 3·45. Infusible, but loses colour before the blowpipe. When powdered, it dissolves completely in boiling hydrochloric acid, and readily in sulphuric acid with evolution of heat. It has been found at various localities in Scandinavia.
Yttrofluorite.
[118]—This is a fluoride of varying composition, very similar to yttrocerite, but characterised by the absence of water, and the very small ceria content (1·7 per cent.). It is thus a fluoride of calcium and the yttrium metals.
[118] T. Vogt, Centr. Min. 1911, 373.
Cubic, with poor octahedral cleavage. Colour, yellow to brown and yellowish-green; transparent to translucent, bleached by weathering. Very brittle. Hardness 41⁄2; sp. gr. 3·54-3·56.
It is very similar to fluorspar (except that the octahedral cleavage of the latter is very good), and is regarded by Vogt as an isomorphous mixture of the latter with yttrium fluoride (or with a double yttrium calcium fluoride, which is less probable). This view would account for the variations in composition, and also for the remarkable frequency with which traces of rare earths are found in fluorspar (vide [p. 2]). Yttrocerite is regarded as a similar isomorphous mixture, but containing cerium metals in addition to the yttrium group.
Yttrofluorite occurs in pegmatite veins in granite in Northern Norway, with gadolinite, fergusonite, allanite, fluorspar, and the usual vein minerals.
The other members of this family (see [list]) are:
Fluocerite, a basic fluoride of yttrium and cerium metals.
Tysonite, a hydrated fluoride containing carbonates.