No. 2.] HARRINGTON NOTE OX DAWSONITE. 85 



It reminds one of tremolite, and in the collection of minerals 

 acquired by McGill Colleo-e j'rom the late Dr. Holmes of Mont- 

 real, there are several specimens of it which he had so marked. 



The first specimens of Dawsonite analysed were found to con- 

 tain between five and six per cent, of lime, and there was no 

 evidence to prove that this was not one of the proper constituents 

 of the mineral. Subsequently, however, it was found that the 

 proportion of lime differed widely in different cases, while the 

 ratio between the other constituents was constant. From this it 

 was inferred that the lime really belonged to intermixed calcite 

 which could not be completely separated. This view is fully 

 confirmed by Friedel's examination of the Dawsonite discovered 

 by M. Maurice Chaper in Tuscany, and the right of the mineral 

 to rank as a good species may now be considered as fully estab- 

 lished. Its special interest of course depends upon tlie fact that 

 it is the only well defined carbonate containing aluminium which 

 has yet been met with in nature. 



The Tuscany Dawsonite is stated to occur in minute crevices, 

 both in marl and sandstone, the latter being impregnated with 

 dolomite. Among the minerals associated with it are calcite, 

 dolomite, pyrite, fiorite and cinnabar; and it is said that the 

 miners of the region look upon Dawsonite as a favourable indica- 

 tion in their search for cinnabar. The Tuscany mineral is 

 evidently obtained in a purer condition than ours, and from his 

 analyses Friedel concludes that the composition of the species is 

 represented by AI2O3, Na20, 2 CO2, 2 H2O or, as lie also 

 puts it, AI2 (C02Na)2 (OH)^. 



The following- table gives under I. the results of Fridel's an- 

 alyses ; under II and III the original analyses of the mineral 

 frum McGill Colleire ; and under IV a recent one of that i'ound 

 at the Montreal reservoir. The last it will be seen indicates the 

 presence of a large proportion of calcite : — 



I II III IV 



Carbon dioxide 29.59 29.88 30.72 32 23 



Alumina 35.89 32.84 32.68 24.71 



Soda 19.13 20.20 20.17 15.64 



Water 12.00 11.91 (10.33) 9.06 



Lime 0.42 5.95 5.65 16.85 



Magnesia 1.39 tr. 0.45 tr. 



Potash 0.38 



Manganese dioxide .... .... 0.23 



Silica 0.40 0.84 



98.42 101.56 100.00 99.56 



