Hartley — On the Beryls of Glencullen, Co. Wickloto. 627 



It will be observed that the weathered beryl contains what one 

 might expect — a diminished proportion of bases and a correspond- 

 ingly increased proportion of silica. According to the very careful 

 research of 0. A. Joy " On Grlucinum and its Compounds," fusion 

 of beryls with two parts of potassium carbonate can be successfully 

 carried out. 1 



Fresenius states, " Native silicates of beryllia are completely 

 decomposed by fusing with four parts of carbonate of soda and 

 potassa." 2 



The proportion of alkaline carbonates necessary for the fusion 

 of Grlencullen beryls was found to be not less than six parts. 



On referring to the composition of the beryls of Acworth, New 

 Hampshire, which were the subject of Joy's research, it is to be 

 noted that they contain more silica by one-third, and only one- 

 half the quantity of alumina contained in the Glencullen beryls, 

 thus : — 



Composition of New Hampshire Beryls. 



Si0 2 68-84, A1 2 3 16-47, BeO 13-40 Fe 2 3 1-7. 



Those who are acquainted with the difference in behaviour of 

 silicious minerals, when treated with alkaline carbonates, will 

 acquiesce in the opinion that it is this high percentage of alumina 

 which renders the beryls of Grlencullen so difficult of fusion. 



Taking into account the small proportion of bases present 

 which are capable of replacing BeO, such as 2 - 6 per cent. CaO, 

 3*13 per cent. FeO, and calculating the molecular proportions 

 of the other constituents, I have assigned to the mineral the 

 following formula : — 



2 (A1A-3 Si0 2 ) -2 (Be 2 Si0 4 ) -BeO- A1 2 3 ; 



or, differently expressed : — 



2 (Al 2 Si 3 09) -2 (Be 2 Si0 4 ) -BeAl A. 



From the point of view of their chemical composition these crys- 

 tals are not beryls, but apparently a new mineral with a constitu- 

 tion lying between beryl and chrysoberyl, that is to say between 

 a silicate of alumina and beryllia and an aluminate of beryllia. 



1 American Journal of Science, "vol. xxxvi., p. 83. 



2 Qualitative Analysis. Ninth. English. Edition, 1876, p. 103. 



SCIEN. PE.OC. R.D.S. — VOL. V., PT. VII. 2 U 



