V il4 TRANS. OP THE ACAD. OP SCIENCE. 
Topaz in Utah . By Henry Engelmann. 
Jx During my explorations in Utah as Geologist of the Expe¬ 
dition under Capt. J. H. Simpson, Top. Eng’rs. U. S. A., in 
p 1858 arid 1859,1 observed some remarkably beautiful crys- 
^ tals of Topaz among some detritus of trachytic porphyry. 
They were perfectly colorless, transparent, sharply devel- 
t \ 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) 
oo c : b : a , 
4 c : b : oo a , 
most of them also 
a few only 
ooc : b : 2 a , c : oob: : ooa 1 , 
2 c : b : a ; 
2 c : b : ooa, c:b:a ; 
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 
crys tals e xa mined in, reg a rd to pyro - electr icity and jaolari^a- 
