In 1907 Hussak[115] published a paper in which he showed that the mineral named after him was not a new species at all, but a xenotime of prismatic habit. Analyses made at his request by Florence in Brazil, G. T. Prior in London, and Tschernik in St. Petersburg, confirmed the original values given by Gorceix (sulphur trioxide up to 0·25 per cent.). He mentions Brögger’s analysis of the Norwegian specimen in which Kraus and Reitinger had found 2-3 per cent. of sulphur trioxide, but in which Brögger found none. He explains the results of Kraus and Reitinger as due to the addition of barium chloride to the acidified solution of the carbonate fusion of the mineral, by which barium phosphate was precipitated; this was dried and weighed as barium sulphate. Rösler’s tests are declared doubtful; xenotime is not a widely spread rock constituent, the mineral in question being really zircon. [115] _Centr. Min._ 1907, 533. In face of these results, there can be little doubt that the name ‘hussakite’ is unnecessary and undesirable, since the mineral to which it was applied is proved to be xenotime. * * * * * In the alphabetical list, particulars of the following rare earth phosphates will be found: _Castelnaudite_, a variety of xenotime containing zirconia. _Churchite_ and _Rhabdophane_ (Scovillite), hydrated phosphates. _Gorceixite_, an alumino-phosphate of alkaline and ceria earths. _Retzian_, an hydrated arsenate of manganese, calcium and rare earth metals. (_b_) THE HALIDES ~Yttrocerite.~--This mineral is a fluoride of calcium and rare earth metals, with water. A recent analysis by Tschernik[116] gives the formula Ce₂F₆,2Y₂F₆,9CaF₂,2H₂O. Putting the rare earth metals together, this gives 6RF₃,9CaF₂,2H₂O, or R₂Ca₃F₁₂,²⁄₃H₂O. Yttrocerite is of interest since it was probably in the analysis of this mineral by the discoverers, Berzelius and Gahn, that the double sulphate method of separating the yttria from the ceria earths was first employed[117] (_vide_ p. 156). [116] _Abstr. Chem. Soc._ 1907, ~92~, ii. 362. [117] _Schweigg. J._ 1816, ~16~, 244. 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.