pi al 3 
J. W. Mallet on Brewsterite. 49 
It is strange that in Thomson’s Outlines of Min., Geol., &c., the 
analysis of Connell is given with altogether different figures— 
thus: ; 
52°400 
Alumina, 15-918 
Baryta, 5°827 
Strontia, 7709 
ime, - - - - 1007 
Water, - - - - - 208 
Peroxyd iron, - - : -  12°584 
95°653 
Dr. Thomson remarking at the bottom of the page that the spe- 
cimen analyzed by himself consisted of fine erystals 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 chlorid of strontium, 
in aleohoi—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 brewsterite 
to heulandite is considered. The two species should in all prob- 
ability 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 
Sate =) 
agree. 
Thave recently analyzed some fine specimens, from the original 
locality—Strontian in Argyleshire, Scotland—and the results 
appear fully to establish the chemical as well as crystallographic 
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 an eighth of an inch in length—most 
of them were much smaller, The following measurements were 
obtained—using the lettering of Dana. 
O: 3-1 = 175° 49’—175° 53’—175° 55’ 
47: $4 =171° 43’—171° 40’. 
a: i= 166° 1s", 
O: 1-4 (2) = 157° 23’—157° 1'7’—157° 20’—157° 29’. 
T: i-4 = 112° 13’—112° 17/—112° 12. 
The spec. grav. was found = 2°453. 
For analysis the crystals were carefully broken off, and picked 
clean from any dust of the accompanying rock. In one case, 
the mineral was fluxed with carbonate of soda, so as to ensure 
perfect decomposition, and consequent purity of the silicic acid 
SECOND SERIES, Vor. XXVIII, No. 82.—JULY, 1859. 
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