189] Mineralogy and Petrography. IIQI 
temperature remains nearly constant. The birefringence is also sub- 
jected to a sudden change at this temperature. Other experiments to 
be made in this same line will undoubtedly show that 570° is a critical 
temperature for the mineral, above which it loses its characteristic 
properties. Cleavages parallel to R and —R, and less perfect ones 
parallel to oP and oP, have been detected by Mallard * in thin plates 
of quartz. The discovery confirms the suspicion that the mineral 
possesses obscure cleavages, usually noticeable only when fragments of 
it are heated and plunged into cold water. In an article in a recent 
Bulletin of the U. S. Geological Survey, Mr. Hillebrand 7 gives the 
results of analyses of some rare zirconium minerals found in the 
granitic debris of Devil’s Head Mountain, Douglas Co., Colo. He 
also records the analysis of a white dery/ from the gangue of a cassiter- 
ite vein at Winslow, Me. The composition of the beryl is: 
SiO; TO ALO; Te, BeO MgO»: (KEGLO NaO- LLO 
65.241, id . 35450. .31. 695.03 . 09 .14 .87 .16 
H,O Sp. Gr. 
1.80 2.707 
Although specimens of /yroZ/fe recently obtained at the Mammoth 
Mine, Utah, are sufficiently well crystallized to afford Prof. E. S. 
Dana data for the determination of the ratio between their lateral 
axes, it has not been possible to decide upon their chemical composi. 
tion. The crystals are in flat tables, united into fan-like groups. They 
are orthorhombic, with their optical axes in the brachypinacoid. Their 
double refraction is negative and 2:4—.9325:1. An analysis by 
Mr. Hillebrand yielded : 
CuO CaO As,O, H,O BO Feo., Ins: 
45.08 6.78 28.52 17.21 2.23 à » 
But this is not capable of representation by a rational formula. 
The characteristics of 2eZyerase have been defined with some accuracy 
by Messrs, Hidden and Mackintosh.” "The material investigated was 
obtained in the zircon region in Henderson Co., N. C., and from the 
Upper Salida River, S. C. The mineral occurs in rough crystals 
bounded by o P3, Pæ, 2P%, P3, and J4Peo, the latter new to the 
M [b,, p. 119. 
15 Tb., p. 123. 
16 Tb., p. 61. 
17 Bull. No. 55, pp. 48-55. 
18 Amer. Jour. Sci., Apr., 1890, p. 271. 
19 Amer. Jour. Sci., Apr., 1890, p. 302. 
December.—8. 
