153 



The values obtained are: 



a 



Red 1,5575 



Yellow .... 1 ,5600 

 Green .... 1,5632 



•2V 



Red 



74° 2' 



ß 





r 



Y—a 



1 ,5620 





1 ,5700 



0,0125 



1,5650 





1 ,5739 



0,0139 



1,5674 





1,5766 



0,0134 



axial angl 



es are calculatec 



Yellow 



Green 





75° 



12' 



77° 





As the acute angle of the optic axes is bisected by the 

 direction of the least velocity of light, the mineral is optically 

 positive. 



The dispersion takes place according to the formula 



p < V. 



The analysis which Lind ström performed on elpidite 

 gave the following results. 



ZrO, 

 FeO . 

 CaO . 

 Na^O 

 K,0. 

 Щ0. 

 CI . . 



59,44 

 20,48 

 0,14 

 0,17 

 10,41 

 0,13 

 9,61 

 0,15 



100,53 



From this is calculated the formula 



Na.2 0-ZrO.,'ZH^O-$ Si 0^ . 



What causes some difficulty in this case is the con- 

 siderable percentage of water. The fact is that on micro- 

 scopical examination the mineral is seldom found to be fresh. 

 Apart from the rarely occurring small and clear crystals, it is 



