Characters of the Cyanite and Sillimanite. 159 
The crystals afforded by this locality, which as yet has 
been imperfectly explored, resemble, very strikingly, in their 
modifications and colour, those from Saxony, but are gene- - 
tally of much larger dimensions, and appear to constitute a 
greater proportion of the rock in which they occur. 
New-Haven, Dec. 22, 1826. ; 
IV. A comparison of the crystallographical characters of the 
Cyanite and Sillimanite ; by Cuas. U. SHeparD.—Hav- 
ing noticed, in Haidinger’s edition of Moh’s Mineralogy, the 
following remarks concerning the Sillimanite, 1 was led for 
some time to consider the distinct nature of this substance as 
highly questionable. 
“* Its analysis agrees exactly with that of prismatic dis- 
thene-spar, by Klaproth. N t erystallographical descrip 
tion is given, but the angle of 106° 30’ is very near the in- 
cidence of P on M, 106° 15’, in that species ; also the speci- 
fic gravity is not much different, and the great hardness may, 
perhaps, be accounted for by the want of a more general 
diffusion of correct methods for ascertaining this property. 
Sillimanite is, therefore, probably, a variety of the prismat- 
ic disthene spar.”’ oc * 
am happy to say, however, that a recent opportunity of 
examining some excellent crystals of this mineral has fully 
satisfied me, that it cannot be identified with the prismatic 
disthene-spar, or cyanite: and that it will, most probably, 
with the greatest propriety, continue to bear its present name. 
_Cyanite, as is well known, is crystallised in irregularly 
i ommonly have their . 
edges replaced by planes. _ It possesses three tleavages : two 
isin the direction of what are regarded its terminal planes, 
thus giving rise to a doubly oblique prism—its primary form, 
whose angles are, 
= M on T - - 106° 18! 
aie 
- - 93 16 
