R. B. Higgs — Composition of Tourmaline. 



49 





Si : 



B : 



B(i) : 



RO : 



O 



Kumford A. . 



1 



•46 



4-48 



5-01 



5-18 



Brazil A 



1 



•47 



4-45 



5-12 



5-26 



Auburn A. _ _ 



1 



•46 



4-43 



4-83 



5-10 



Brazil B 



1 



•47 



4-50 



4-92 



5-17 



Auburn B 



1 



•48 



4-48 



4-80 



5-11 



Brazil C. 



1 



•45 



4-42 



4-93 



5-15 



Rurnford B... 



1 



•48 



4-44 



4-95 



5-20 



Auburn 



1 



•46 



4-50 



4-99 



5-20 



Paris . 



] 



•45 



4-47 



5-09 



5-21 



Auburn I). .. 



1 



•48 



4-50 



5-01 



521 



Brazil D 



1 



•48 



4-50 



5-02 



5-21 



Haddam. 



1 



•50 



4-51 



5-00 



5-24 



Nantic Gulf. . 



1 



•51 



452 



5-00 



5-25 



Stony Pt 



1 



•51 



4-19 



5-01 



5-41 



Pierrepout. __ 



1 



•51 



4-52 



4-77 



543 



Monroe 



1 



•46 



4-43 



4-89 



5-12 



Orford. 



1 



•48 



4-48 



4-99 



5-20 



Gouverneur. _ 



1 



•50 



4-51 



473 



5-10 



Hamburg. 



1 



•51 



4-50 



5-08 



5-30 



Dekalb. 



1 



•50 



4-51 



5-08 



5-29 





1 : 



•48 : 



4-47 : 



4-96 



520 



II 



74 

 70 

 72 

 66 

 71 

 66 

 64 

 74 

 70 

 70 

 68 

 60 

 G8 

 68 

 63 

 69 

 68 

 68 

 59 

 66 



67 



Alk. 

 •28 

 •31 

 •28 

 •31 

 •30 

 •32 

 •30 

 •28 

 12 

 •12 

 •13 

 •12 

 •12 

 •10 

 •09 

 •15 

 •13 

 •10 

 •06 

 •08 



Except in two or three cases the ratios of Si : B : R( 1 ) : O ap- 

 proximate closely 1 : i : ■§■ : 5. The oxygen, in excess of the 

 amount exactly represented by the ratio (5), having been ab- 

 sorbed in an A1=0 group. These ratios give as a general tour- 

 maline formula the simple boro-orthosilicate R 9 B0 2 2Si0 4 , 

 which resolves itself into the graphic formula 



/BO, 



R^sio; 



R=siO, 



>R 



The R 9 includes the constant H = R± (Li, Na, K), varying be- 

 tween the limits Ri and R§, (Ca . Mg) varying from R to R 3 , 

 Fe varying from R to Rf and (Al, A1=0) varying from R 4 to 

 R 7 . On the other hand the ratios Si : B . R( 2 ) : O are about as 

 1 : \ : 10 : 5*20, which would give the equally simple general 

 formula R 10 BO 2 2SiO 4 , where R 10 includes the above constant 

 and variables excepting that OH replaces the A1=0 group and 

 Al accordingly varies between the limits R 5 and R 8 . If we 

 expand, in order to bring out the hydroxy 1 ratio, we have 

 12Si0 4 , 6B0 2 , R M H B (OH),=Si :B:R:0=1:J:5: 5-25. 



Between these two views there are at present no means at 

 hand of deciding. Could we find out that the water is not 

 all driven off at the same temperature or something of the kind, 

 the knowledge would favor the latter assumption. 



Experiments to this end are desirable. But whichever pos- 

 tulate we make, the following special formula may be taken as 

 representing typical compounds of the three varieties : 



Am. Jour. Sci— Third Series, Vol. XXXV, No. 205.— Jan., 1888. 

 4 



