26 Sypney H. BALL: 
occurs in apparent pegmatitic intergrowths with it (Fig. 10). A sample 
of this pegmatite, which appeared from inspection to be a pegmatitic 
intergrowth of cryolite and felspar was examined microscopically. 
Present as accessory minerals were good crystals of zircon and a little 
apatite, and an irregular area of hematite in part altered to limonite. 
The most abundant mineral is microcline, presumably a soda-rich 
variety to which the cryolite is subordinate in quantity. The two minerals 
in places have mutually interlocking edges and elsewhere felspar forms 
ET 
о 
5 oe 
Fig. 13. Pegmatite of felspar and cryolite. 
С = cryolite. К = microcline. H = hematite. Z = zircon. 
Magnified 60 x. 
crystal faces against cryolite. It appears to be, on the average, 
younger than the microcline in this particular sample, and probably 
in part even replaces it. Evidently the cryolite, in part, is older than, 
in part contemporaneous with and, in part, younger than the felspar 
(Figures 11, 12 and 13). Other constituents of this pegmatite are side- 
rite, cassiterite, wolframite (ferberite), molybdenite, pyrite, chalcopyrite, 
zincblende, galena and fluorspar: other observers have noted, in addition, 
columbite, tantalite and arsenopyrite. Some of these minerals in vugs 
occur in fine crystals. 
Тотлоз THOMSEN found that some of the fluorspar associated with 
the eryolite contains a little yttrium fluoride and that upon heating 
