146 SeyhcrCs Analysis of Pyroxe/ie, 



lowing results per 1000, viz. "Silica 0.560; Lime 0.151 5 

 Proto:iide of Manganese 0.135; Peroxide of Iron O.lOO; 

 Oxide of Zinc 0.610 ; Alumine 0.020. Loss by calcina- 

 tion 0.010=0.986 ;" and the substance was accordingly de- 

 ternnined to be a Tris-ilicate. This nnineral was separa- 

 ted by these gentlemen from the Pyroxene of Haiiy, be- 

 cause they say "its cleavages are essentially different j'' 

 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 

 appears 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 

 Academy of Natural Sciences. 



Mr. Keating's memoir was republished in the Annales 

 des Mines, Vol. 7, p. 415, and in a note, p. 419, we 

 have the high authority of Professor Berthier, for consid- 

 ering the Jeffersonite a new mineral species; his opinion ie 

 however, entirely founded on the results of Mr. Keating's 

 analysis : he says, " La composition de la Jeffersonite ne 

 permet de confondrc ce mineral avec aucune espece connue. 

 Cette pierre differe essentiellement du pyroxene quoiqu' 

 elles'en rapproche par sa forme, en ce qu'elle est composee 

 de Trisilicates, tandis que les pyroxenes ne contiennent que 

 des Bisilicates." 



I 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 gratiiied 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- 

 terised 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 

 regent fracture Is resinous. Opake, crystalline, presenting 



