114 
TRANS. OF THE ACAD. OF SCIENCE. 
Topaz in Utah, By Henry Engelmann. 
During my explorations in Utah as Geologist of the Expe- 
dition under Capt. J. H. Simpson, Top. Eng’rs. U. S. A., in 
1858 and 1859, I observed some remarkably beautiful crys- 
tals of Topaz among some detritus of trachytic porphyry. 
They were perfectly colorless, transparent, sharply devel- 
oped, and of great lustre. They were all short columnar. 
The largest of them measured scarcely one third of an inch 
in the direction of the basal cleavage, which was highly per- 
fect. I observed ten modifications : all crystals exhibited 
(according to Prof. Rose’s designation) 
ooc : b : a , 
4 c : b : 00 a , 
most of them also 
a few only 
oo c : b : 2 a 
2 c : b : a 
2 c : b : oo a 
2 c : 00 b : a 
c : oo b : : oo a 1 , 
c : b : a ; 
and 4 (?) c : b : a . 
As in none of the crystals were both ends developed, I 
could not ascertain whether they were hemihedral, as is most 
common with topaz. The hardness of the mineral is =8. It 
is infusible before the blowpipe ; and when strongly heat ed 
is coated with small blisters, but does not show any change 
of color. It exhibits the reactions of fluorine, alumina, and 
silex. ISTo tests were made for other elements, nor were the 
crystals examined in regard to pyro-electricity and polariza- 
tion of light. They exhibit double refraction quite plainly. 
The locality of the mineral is near lat. 39° 40', long. 113° 
30' west of Greenwich, west of south of Salt Lake, in Thom- 
as’ range of mountains, on Capt. Simpson’s return trail. Cir- 
cumstances prevented me from obtaining more than a few 
crystals, which are now deposited in the collection of the 
Smithsonian Institute; a few others are also in the hands of 
members of the party. We were travelling at the time by 
forced night marches with nearly worn out animals, seeking 
to gain a spring of water in a distant range of mountains. 
This desert was then entirely unexplored. I have but little 
doubt that more interesting materials are to be found at the 
same point. 
The mountains of the former Territory of Utah promise a 
rich yield to the mineralogist. We know already of gold and 
silver ores in the east, west and south part of that district ; 
of copper and lead ores in the south, and I have discovered 
the latter also in the centre of it; of specular iron ores and 
native sulphur in the Rocky Mountains and near Little Salt 
Lake ; of rock salt in the mountains south-east of Utah Lake; 
of native alum near Salt Lake; of various other salts in the 
deserts ; and of silicates, composing the granites, porphyries, 
diorites, trachytes, and lavas, nearly over the whole area. 
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