Fergusonite, an Endothermic Mineral. 



325 



u Fergusonite, an Endothermic Mineral." By WlLLlAM Ramsay, 

 Ph.D., LL.D., Sc.D., F.R.S., and Morris W. Travers, B.Sc. 

 Received December 15, 1897, — Read January 20, 1898. 



The mineral fergusonite, discovered by Hartwall, occurs in felspar 

 and mica deposits, in the same manner as most of the rare Norwegian 

 minerals, such as euxenite, orthite, samarskite, &c. The position in 

 which such minerals are found, embedded in masses of felspar, or 

 encrusted with mica, leaves the question of their origin an open one. 

 Whether they are deposited in the felspar by water, or whether they 

 are contemporaneous with the felspar, is a matter of speculation. 

 Fergusonite is a black lustrous mineral, not unlike obsidian in out- 

 ward appearance, but of considerably higher density. Seen under 

 the microscope, even with the highest power, there is absolutely no 

 sign of crystalline structure, though in thin slices the substance 

 is translucent, and transmits yellow-brown light. It is, however, 

 macrocrystalline, occurring in quadratic sphenoids. It is quite 

 homogeneous, and displays no sign of cavities. Like similar mine- 

 rals, it contains helium, which is expelled on the application of heat. 



But this mineral presents a peculiarity, which has led us to publish 

 this note. When heated to a temperature not exceeding 500° or 

 600°, it suddenly becomes incandescent, and evolves much of its 

 helium; while its density decreases. 



The analysis of the mineral was kindly undertaken by Miss Emily 

 Aston, to whom we desire to express our indebtedness. The mineral has 

 been previously analysed by Hartwall, its discoverer, and by Weber, 

 and, for the sake of comparison, we quote the earlier analyses* : — 



Composition of Fergusonite. 



Miss Aston. Hartwall. Weber. 



Oxides of niobium and tantalum .... 40*95 47*75 48*84 



Oxides of yttrium, erbium, &c 31*09 41*91 38*61 



Oxides of cerium, &c , 13*87 4*68 3*05 



Uranium dioxide 3*36 — 0*95 0*35 



Uranium trioxide 3*81 — — — 



7*17 



Titanium dioxide 4*56 — — 



Zr0 2 — 3*02 6*93 



Silica , 1*42 — — 



Ferric oxide 1*55 — — 



FeO — 0*31 1*33 



Lead oxide 0*16 — — 



Sn0 2 ., TOO 0*35 



Copper oxide 0*12 — — 



100*89 99*62 99*46 



* Rammelsberg's ' Mineralchemie,' p. 401. 

 VOL. LXT1. 2 A 



