14 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 64 



lamellae, makes it hard to accept the idea that the mineral owes its 

 nonisotropic character to anomalies explained by internal strain. 



A sample for analysis was selected carefully and its homogeneous 

 character and purity were established microscopically. The analysis 

 gave the following composition and ratios: 



Analysis and ratios of analcite. 



The above ratios are not satisfactorily close to whole numbers to 

 conform to the analcite formula given by Dana, both water and 

 silica being high. Parsons ^ recently, in discussing the composition 

 of analcite from Nova Scotia, has shown that all of the analyses of 

 analcite given by Dana can be satisfactorily interpreted by the as- 

 sumption that the mineral is composed of an isomorphous mixture of 

 two compounds of the composition (A) Na2O.Al2O3.6SiO2.3H2O and (B) 

 Na2O.Al2O3.2SiO2.H2O. Considered from this standpoint the Idaho 

 material may be regarded as made up of almost exactly two parts 

 of (A) and one of (B) molecularly, as shown by the following table in 

 which the condensed figures of the analysis are given in column 1 

 compared with the percentages calculated for a mixture of the 2 : 1 

 composition in column 2. 



The paragenetic position of the analcite is late, as it grew between 

 the laminiE of calcite or occupied cavities left by removal of calcite 



' Arthur L. Parsons. Univ. of Toronto Geol. Series No. 14. Contributions to Canadian Mineralogy, 1922 , 

 pp. 34-38, 1922. 



