Crystallization of Parisite. 541 



o)>e slight. For crystals l mm thick the dichroism and absorp- 

 tion are but slightly greater. Upon alteration the crystals 

 become filled with a dusty product, are less transparent and 

 often exhibit a brownish or brownish red stain of varying 

 intensity. 



The indices of refraction were determined by the immersion 

 method, using a barium-mercuric-iodide solution. The deter- 

 minations were made on a number of perfectly clear, small 

 crystals chosen on account of the uniform development of their 

 prism zones ; also upon one larger crystal (l^ nim in diam.) ter- 

 minated by a perfect basal plane which made it possible to 

 orientate the crystal and cut a section parallel to the prismatic 

 axis. An attempt was made to measure the indices directly 

 upon this crystal by means of the Abbe refractometer, but 

 without success, owing to the small size of the section and its 

 low degree of transparency. The fine striations parallel to the 

 edge between the base and the prism stand out very sharply 

 under the microscope and make it possible to orientate the 

 crystals with great accuracy on the microscope stage. The 

 values obtained with sodium light are given below, also those 

 heretofore given for parisite as determined by Senarmont and 

 those for synchisite according to Flink. 



Parisite, Quincy Parisite, Muso Synchisite, Greenland 



Warren Senarmont Flink 



e= 1-757 1-670 1-7701 



co= l-676(±0-002) 1-569 1-6742 



e-o)= 0-081 0-103 0-0959 



The Montana parisite, analyzed and described by Penfield 

 and "Warren (loc. cit.), also crystals from Muso valley taken 

 from the mineral collection of Harvard University, were tested 

 by the immersion method and their indices were found to cor- 

 respond to the values given for the Quincy mineral. The older 

 values given for the Muso mineral appear to be quite wrong. 

 The ordinary rays for parisite and synchisite are almost iden- 

 tical. The extraordinary rays appear to differ by - 0131. 

 While the extraordinary ray for the Quincy mineral is prob- 

 ably not as accurately determined as the value for the ordinary, 

 the error can hardly be as great as 0-0131 and the difference 

 between the two minerals for this constant may perhaps be a 

 real one. 



Chemical composition of Parisite. — About a kilo of fine- 

 grained material recovered from the fragile lining of the cen- 

 tral pockets was carefully washed and fractioned by means of 

 screens, an electro magnet, and heavy solutions until a fraction 

 was obtained weighing about ten grams and consisting largely 

 of parisite mixed with more or less aegirite, anatase, feldspar 

 and quartz. From this about three grams of clear yellow or 

 atnber- colored crystals were separated by hand-picking under 



