Br. Thomson on some New MmeraXt, 67 



is obviously a triple sosquisilicato. Its constitution may be repre- 

 sented by the formula, 8 (MgS'^) + 4 (/ S'^) + 3 (A1S'«) + 18 Aq. 

 10. The next mineral which I shall notice is one which occurs in 

 the beds of iron ore at Franklin in New Jersey, and was first noticed 

 by Messrs. Keating and Vanuxen about the year 1822 under the 

 name of Jeflfersonite. Keating made an analysis of it, the result of 

 which induced me to place it among the magnesian minerals, and 

 intimate in connection with pyroxene and amphibole. But having got 

 a specimen of it througli the kindness of Dr. Torrey of New York, I 

 subjected it to a new analysis. The result was so diflferent from Mr. 

 Keating's, that it became evident that the position which I had 

 assigned it was a wrong one, and that in reality it was a quadruple 

 salt, consisting of silica united to the four bases — lime, alumina, iron, 

 and magnesia. 



The colour of Joffersonite is dark olive green, passing into brown. 

 It is foliated, and according to Keating may be cleaved in various 

 directions. The specimen in my possession is an imperfect four sided 

 prism ; but the faces are not smooth enough to admit of measurement 

 The lustre is resinous and almost semi-metallic ; the streak is gray, 

 and the powder light green. It is rather harder than fluor spar, 

 though softer than apatite. The specific gravity is 3'51. Before the 

 blowpipe it fuses readily into a dark coloured globule. Its consti- 

 tuents are 



Silica, .... 44-50 

 Lime, .... 22-15 



Alumina, .... 14*55 

 Protoxide of iron, . . 12*30 

 Magnesia,". . . . 4*00 



Moisture, .... 1*85 



99-35 

 The constitution may be represented by the formula, 4 (Cal.S) + 

 4 (AIS) + 2 (/S*) + Mg S' so that it differs essentially in its com- 

 position from both pyroxene and amphibole. 



I6th Novemhevy 1842, — T?ie PiiEsroENT in the Chair, 



Mr. Liddell, the Treasurer, presented his account, exhibiting an 

 expenditure of £33, and a balance of £60 in banker's hands. The 

 Librarian also brought forward his account, which showed the receipt 

 of £50 for the library fund, and a balance of £15 in hand. 



The following gentlemen were elected members of the society: — 

 Dr. Hugh Colquhoun, Dr. Alexander Mitchell, Mr. Duncan Anderson, 

 Mr. Georgo Thomson, Mining Engineer. 



