Foi'd — Effi'ct of the Presence of Alkalies in Beryl. 129 



locality of Pala and, thinkino:, that from this specimen botli 

 indices might be determined, an orientated prism was cut from 

 it and measnrements of the two indices made. The values of 

 the indices for the ordinary rays as determined from the two 

 prisms were, however, quite different, that of the Pala beryl 

 being the higher. This suggested that the two specimens 

 differed in the amount of the alkali oxides which they contained 

 and this was proven by sacrificing enough of the crystal to 

 permit the making of a determination of the alkalies present. 

 The Pala beryl was found to contain 3'77 per cent of alkali 

 oxides of which over half of a per cent proved to be csesium 

 oxide. 



The rose-colored beryl from Madagascar contained still more 

 alkalies, -I'GS per cent in all, 1"60 per cent of which was caesium 

 oxide. The material analyzed showed no crystal faces and the 

 prism for the nieasnrement of the indices of refraction, also, had 

 to be cut at random. It happened, however, that it nuist have 

 been cut with its edge very closely parallel to the direction of 

 the optical axis for the birefringence shown was quite what 

 would have been expected through the study of the various 

 other results. In order to prove the orientation of the prism, a 

 section was cut from it at right angles to its faces and, in conver- 

 gent light, this section showed an unaxial interference figure 

 nearly symmetrically centered in the field of conoscope. So the 





I 



II 



III 



IV 



V 



Mesa Grande 



Willimantic 



Pala 



Madagascar 



Hebron 





Analyst, 



Analyst, 



Analyst, 



Analyst, 



Analyst, 





Ford 



Penfield 



Ford 



Ford 



Wells 



SiO, ... 



64-98 



65-72 



undet. 



62-79 



62-44 



AiA .. 



17-86 



18-40 



undet. 



17-73 



17-74 



FeA - 



- - - _ 















0-40 



FeO ... 







0-26 















MnO... 







0-12 







trace 







BeO ... 



13-42 



13-08 



undet. 



11-43 



11-36 



Cs,0_-. 









0-57 



1-70 



3-60 



K,0.... 



0-18 



0-12 



0-28 











Na„0 .. 



0-84 



0-75 



1-59 



1-60 



1-13 



Li^O ... 



0-46 



0-28 



1-33 



1-68 



1-60 



Ign 



2-16 



2-06 



undet. 



2-65 

 99-58 



2-03 



Total .. 



99-90 



100-79 





100-30 



Total 













alkalies 



1-48 



1-15 



3-77 



4-98 



6-33 



Specific 













gravity 



2-714 



2-73 



2-785 



2-79 



2-80 



CO =^ 



1-58157 



1-58455 



1-59239 



1-59500 



1-59824 



e = 



undet. 



1-57835 



1-58488 



(1-58691)* 



1-59014 



-€= -00620 -00751 ( -00809)* -00810 



* Approximate. 



Am. -Jour. Sci. — Fourth Series, Vol. XXX, No. 176.— August, 1910. 

 9 



