Spodumene and its Alterations. 343 



Theoretical Constitution. — The following atomic relationships 

 may be thence deduced, reckoning R n =2 K. 



R n 



: K 



R 1 



: R: 



Si: H 



Si : 



H a 



1 : 



1.0 



1 



: 1 : 



2.5 : 2.9 



1: 



: 0.6 



This corresponds to the formula for the half-silicate, which 

 Rammelsberg writes — 



H 6 K 2 ^3r 2 Si 5 O 2 ". 



if all the hydrogen be basic. Or, after his other plan, with no 

 basic hydrogen, it may be written — 



2 R ^ 2 Si 5 O 17 + 3 aq. ) 



3 K 2 :A± 2 Si 5 O 17 + 3 aq. f 



But in my opinion, for a reason stated beyond, it is probable 

 that only one-third of 'the hydrogen is basic, and that the true 

 empirical formula should read — 



H 2 K 2 &? Si 5 1S + 2 aq. 

 or 



R\ 6 Si 5 O 18 + 2 aq.= 1 1 ^ | qI | + 2 aq. 



i. e., two molecules of the normal and three of the half-silicate, 

 plus two of water. 



Killinite thus appears to bear a close chemical relationship to 

 Iolite in its forms altered by hydration, e. g. Fahlunite, Chloro- 

 phyllite, etc., and to possess the rational formula, 



9 ]K 2 Si O 3 ) ... f (H, K) 2 Si 4 ) . „ 

 * ( te Si 3 O 9 [ + d } £t 2 Si 3 O 12 j" + l ac l- 



The theoretical percentage composition, calculated from the 

 empirical formula, will be as follows: 



