146 A. WV. Alling—Topaz from the Thomas Range, Utah. 
Art. XVIII.—On the Topaz from the Thomas Range, Utah ;* 
by A. N. ALLING. 
THE topaz crystals under examination were selected out of a 
considerable number in the cabinet of Professor Brush, from 
the locality in Utah in the Thomas Range, 
forty miles north of Sevier Lake, where they 
occur in rhyolite+ They vary from 3™ to 
10™™ in length, and are perfectly clear and 
colorless. The planes for the most part are 
very highly polished, though vicinal planes 
appear in a number of cases to disturb the 
accuracy of measurements. The habit to 
which most of the crystals conform is shown 
in the figure. ‘The observed planes are: 
Pinacoids 6 (010, 7-%), c (001, O); prisms m (110, 7), J (120, 2-3); macrodome d 
(201, 2-2); brachydomes f (021, 2-2), y (041, 4-2); pyramids 7 (223, 3), uw (111, 1), 
o (221, 2), e (441, 4). 
The following angles, each representing the mean of a num- 
ber of careful measurements with a Fuess compound goniome- 
ter, were taken as fundamental : : 
yay’ 041.041 = 124° 417 45" 
Ooesoy GUL C= SOs OC, 
| 
From these angles the axial ratio was calculated, viz: 
i: b:¢ = 05285: 1: O-47715, 
It is interesting to note that these values approximate very 
closely to those obtained by von Kokscharow,t upon the Sibe- 
rian crystals; he gives: 
wi: ¢ = 0°52854 : 1: 0-47698, 
On the other hand, the axiai ratios for crystals from Hhren- 
friedersdorf, Altenberg, Schneckenstein and Brazil, vary from 
both more or less widely (compare Griinhut, Zeitsch. Kryst., 1x, 
113). Some of the calculated and measured angles on the 
Utah crystals, in addition to those given above, are as follows: 
Calculated. Measured. 
Cie ROOM M02 14325397 43° 397. 
CAG. 001,223) = 1347 1157 34° 157, 
cao 001,221 = 63° 58” 63° 517. 
CRO WOON ACAU 3 1G> WeeY WO? 1HZ 
mre’ ub Wt == 9° 07 392 1s 
0on0°” 221.221 = 49° 39! 49° 397, 
ay Nel OLIN AAI 1592 14 59° 97, 
mam! 110.110 = 55° 437 5Ao 447, 
* Abstract of a college thesis written June, 1886. 
+ Compare W. Cross, this Journal, xxxi, 437, June, 1886. 
{ With v. Kokscharow the vertical axis has double the length taken here. 
