352 Topaz. 
Argv. XV.—Topaz. 
Lazonarory or Yair Corzeas, Jan. 10th, 1826. 
FO PROPESSOR SILLIMAN. 
To the interesting mineral from the town of Huntington in 
this State, which you recently put into our hands for exami- 
nation, we have devoted as much time and attention as were in 
our power, availing ourselves of tlie instruments ahd re-agents, 
_&c. of this Laboratory, and of your occasional advice and as- 
sistance. Had yourduties permitted you to examine it your- 
self, its characters would no doubt have been more accurate- 
ly and clearly exhibited, but such as we have found them, 
we present them for your disposal, 
1. Crystallization. 
This mineral oceurs both massive and crystalline, always 
however distinctly foliated in one direction. The crystals 
are either four or eight-sided prisms. The largest crystals 
are four-sided, and the angles of the base oblique; but not 
to be measured with accuracy, on account of their imperfec- 
tion. Inno instance have we found a crystal sufficiently per- 
fect to ascertain its terminations, though some of the termi- 
nating faces are visible. A fragment ofan eight sided prism, 
was found by a common goniometer to measure as follows: 
The two most acute angles, each - - 92° 
The two next less acute, do. - < 125° 
The four most obtuse, do. < - 162° 
The measures of the corresponding angles ofan eight-sided 
prism of the topaz, as given by Cleaveland, 2d edition Min- 
eraology, p- 292, are, 93° 6/—124° 22’—161° 16’; and when 
we consider that the specimen we measured was quite imper- 
fect, so that it was scarcely possible, without a reflecting gon- 
iometer, to ascertain the angles nearer than one or two de- 
grees, we can have little doubt, that the crystal described by 
Prof. Cleaveland, and that under consideration, are identical. 
Several other crystals, partly imbedded in the gange, pre- 
sented one or two angles of about 120°: and we presume that 
they are six-sided prisms, though we do not state this as cer- 
faine 
