146 Seybert’s Analysis of Pyroxene. 
lowing results per 1000, viz. “Silica 0.560; Lime 0.151 ; 
_ Protoxide of Manganese 0.135; Peroxide of Iron 0.100; 
Oxide of Zinc 0.010; Alumine 0.020. Loss by calcina- 
tion 0.010=0.986 ;”’ and the substance was accordingly de- 
termined to be a Trisilicate. This mineral was separa- 
ted by these gentlemen from the Pyroxene of Hay, be- 
cause they say “its cleavages are essentially different 5” 
that it is remarkably different from pyroxene in being de- 
cidedly harder; that these minerals differ in their specific 
gravities, and add, “ the chemical analysis offers another 
important difference, in the absence of Magnesia, which 
ppears to be essential to pyroxene.” ; 
Dr. Troost, of this city, has lately paid particular atten- 
tion to the crystallographical characters of this mineral, and 
found, that they perfectly coincide with those of well char- 
acterized pyroxenes ; a full account of his investigations, 
will, very soon, be published in the Transactions of the 
{ was, therefore, anxious that a further examination of 
this subject should be made, more especially, as so much 
depended upon the results of the chemical analysis. It 
would have gratified me very much, if this could have been 
done by Mr. Keating; but his absence, from this city, 
will, probably, continue several months ; I therefore deter- 
mined to undertake it myself. 
The specimen, which I examined was shown to Mr. 
Vanuxem. Without any hesitation, he said it was well charac- 
erised Jeffersonite from New-Jersey. The recent fracture, 
of this mineral, is of a very deep olive colour; the exter- 
nal surface, owing to exposure, is deep brown; colour of 
the powder, yellowish brown. Externally, it is dull ; its 
recent fracture is resinous. Opake, crystalline, presenting 
