Mr. J. W. Mallet on Brewsterite 219 



Silica 52-400 



Alumina 15-918 



Baryta 5-827 



Strontia 7-709 



Lime 1-007 



Water -208 



Peroxide of iron . . . 12 584 



95-653 



Dr. Thomson remarking at the bottom of the jmge that the spe- 

 cimen analysed by himself consisted of fine crystals carefully 

 selected, while that examined by Mr. Connell was a mixture of 

 amorphous and crystallized mineral. 



The method for the separation of baryta, strontia, and lime, 

 employed by Connell — probably by both analysts — namely, the 

 solution of nitrate of lime, and afterwards of chloride of stron- 

 tium, iu alcohol — has given place to more reliable processes; and 

 on this account a repetition of the analysis might be desirable ; 

 but it becomes still more so when the close analogy of Brew- 

 sterite to Heulandite is considered. The two species should in 

 all probability have the same general formula, and this has in 

 fact been assigned to them in Dana's 'Mineralogy;' but with 

 the formula for Heulandite these older analyses of Brewsterite 

 do not very well agree. 



I have recently analysed some fine specimens from the original 

 locality (Strontian in Argyleshire, Scotland) ; and the results 

 appear fully to establish the chemical as well as crystallographic 

 relationship with Heulandite. 



The mineral formed crusts of minute crystals upon the surface 

 of gneiss : sometimes these crusts could be detached from the 

 rock by careful blows, but in general they adhered very firmly. 

 Some of the crystals were |th of an inch in length ; most of them 

 were much smaller. The following measurements were obtained, 

 using the lettering of Dana : — 



: f ^ = 175° 49'- 175° 53' -175° 55'. 



^-j:f5 = 171°43'-171°40'. 



/: 7=136° 13'. 



O: l-^(?) = 157°23'-157° 17'- 157° 20'- 157° 22'. 



I: «4 = 112° 13'-112° 17'-112° 12'. 



The specific gravity was found =2-453. 



For analysis, the crystals were carefuly broken off and picked 

 clean from any dust of the accompanying rock. In one case the 

 mineral was iiuxcd with carbonate of soda, so as to ensure per- 



