52 Mr Connell's Description and Analysis of 



From table-spar, the mineral obviously differs in containing 

 water as an essential constituent, and in the relative proportions 

 of silica and lime, table-spar being a bisilicate of lime. From 

 those zeolites which do not contain alumina as a necessary in- 

 gredient, such as apophyllite, and Dr Thomson's wollastonite, it 

 differs, in respect that the quantity of alkali is too small to be 

 viewed as an essential constituent, as well as in the relative pro- 

 portions of silica and base. 



As soon as I had completed the analysis, I sent an account 

 of the result to Sir David Brewster, who was so kind as to 

 examine a few of the optical properties, and to give me the fol- 

 lowing notice of his observations : 



" My Dear Sir, 



" I ought to have thanked you sooner for your letter of the 

 5th December. There can be no doubt that the mineral is a 

 new one, and I have made various ineffectual attempts to obtain 

 crystals from the surface of the large specimen which I have of 

 it, and which I received from Count Vargas Bedemar. The 

 crystallized faces are perfectly distinct, but they he so near the 

 general surface, that it is impossible to detach any fragment 

 without pounding it. 



" I have, however, ground and polished a piece of the tough 

 mass, and have ascertained that it possesses double refraction. 

 It is also opalescent, reflecting a bluish light, and consequently 

 transmitting a yellowish one. I have also found that its powder 

 possesses no pyro-electricity. I cannot help thinking, that, by a 

 careful examination of different specimens, small crystals will be 

 found in some of the superficial cavities. I am, My Dear Sir, 

 ever faithfully yours, 



" D. Brewster." 

 " Belleville, Dec. 26. 1833." 



