Penfield and Foote — Composition of Tourmaline. 119 



It would seem that the mass effect of the complex radical 

 [Al 3 (B.OH) 2 Si 4 19 ], which has a valence of nine, is sufficiently 

 pronounced to control or dominate all types of tourmaline. 

 Thus it apparently makes no difference whether the nine 

 hydrogens are replaced largely by aluminium and to a slight 

 extent by alkalies ; or largely by magnesium and to a slight 

 extent by aluminium and alkalies ; or to about an equal extent 

 by aluminium, iron or magnesium and alkalies ; the result in 

 all cases is the mineral tourmaline, with its characteristic crys- 

 tallization and its peculiar optical and electrical properties. 



The following example (compare the ratio derived from the 

 analysis of the green tourmaline from Haddam Neck, page 

 107) will illustrate the method of determining to what extent 

 the nine hydrogens of the tourmaline acid, H 9 Al 3 (B.OH) a Si 4 19 , 

 are replaced by metals of different valences : 



Ratio. Total hydrogen 



equivalent, or 20 H. 



2(0 H, F) 



18 H. 



3 Al. 



9H. 







A1 2 3 





2-327 





2-327 



1-385 



•942 -f- 



•154 



= 6-1 R"' 



FeO 



•059] 

















MnO 

 MgO 



•056 ! 

 •008 f 



•169 





•169 





•169 -r- 



•154 



= 1-1 R" 



CaO 



•046 J 

















Na 2 

 Li 2 



•068 | 

 •110 j 



•178 





•178 





•178 -4- 



•154 



= 1-2 R' 



H 2 

 F 



•344 [ 

 •060 j 



20) 



•404 



•308 



2 



•096 



9) 



•096 -4- 



•154 



= 0-6 H. 





3-078 



)2-770 



1-385 



<H) 







•154 





1-385 





•154 







From the ratio of the total hydrogen equivalent, /„ (repre- 

 senting two hydroxyls) are deducted. The remainder, 18 H, 

 is divided by two, thus determining the ratio of the nine H's 

 replaced by Al, in the formula. The excess of the aluminium 

 or trivalent metal ratio, R ;// , together with the ratios of the 

 bivalent metals, R 7/ , the alkali metals R' and the excess of 

 hydrogen, H, represent nine H's, which are divided among the 

 different constituents. Thus in the green tourmaline from 

 Haddam Neck 6*1 hydrogens are replaced by Al (R'")? 1*1 by 

 R", 1*2 by R ; and there remains 0*6 excess of basic hydrogen. 



The analyses of Riggs, Jannasch and Kalb, Scharizer and 

 Chatard, given on page 555 of Dana's Mineralogy, together 

 with our own analyses, practically include all varieties of tour- 

 maline which have thus far been investigated, and in the fol- 

 lowing table are given the results of applying the foregoing 

 method of calculation to them : 



