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. II. 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) 



qo c : b : a , ooc:b:2a, c : oo b : : oo a 1 , 



4 c : b : oo a , 2c:b:a ; 



most of them also 2 c : b : ooa, c:b:a ; 



a few only 2 c : oo 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 heated 

 is coated with small blisters, but does not show any change 

 of color. It exhibits the reactions of fluorine, alumina, and 

 silex. No 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. 



