270 Canadian Record of Science. 



This specimen might well be called an analcite-tuff, its clastic 

 nature being apparent at a glance. The large white minerals 

 are analcite (3 to 4 mm. in diameter). A few irregular prisms 

 of a soda-pyroxene occur ; they are, however, almost entirely 

 replaced by calcite and to a lesser extent by what is un- 

 doubtedly secondary analcite. This latter mineral is perfectly 

 clear and colorless, and is unlike the primary analcite in this 

 respect. The fine grained matrix consists of small fragments 

 of analcite and soda-pyroxene. 



Thoulet's solution was used for the separation. On 

 account of the very fine grained matrix a perfectly pure product 

 was not obtained. The result of the analysis, however, as 

 given in table I, No. A., leaves no doubt as to its identity. 



It is interesting in this connection to note the experiments 

 of Clarke and Steiger 1 on the action of ammonium chloride 

 upon silicates. The first mineral experimented on was analcite 

 and their work has thrown considerable light on its chemical 

 composition. When a number of analyses of analcite, as given 

 in text-books like Dana's Manual, are studied, it is at once 

 apparent that they differ in a marked degree from the theor- 

 etical composition. It is not always possible to account for 

 this difference by impure material used or errors of manipula- 

 tion. The results of experiments by Clarke and Steiger seem 

 to show that analcite is not a metasilicate as was commonly 

 supposed, but is a mixture of ortho and trisilicates. In most 

 cases the two salts are commingled in the normal ratio 1:1. 

 With this hypothesis the discrepancies in the analyses become 

 intelligible. 2 The variation from the theoretical composition 

 in the analysis made by the writer is due to an imperfect 

 separation by the heavy solution, as is shown by the presence 

 of iron, calcium and magnesium oxides. For comparison the 

 theoretical composition of analcite is given below, together 

 with three other analyses. 



1. The action of ammonium chloride upon silicates. Bull. No. 207, U.S. Geol. 

 Sur., 1902. 



2. Bull. 207, U.S. Geo. Sur., page 19. 



