-Penfield and Foote — Composition of Tourmaline. 101 



third formula ; to possible inaccuracies in the difficult ferrous 

 iron determinations ; and in part to the fact, as stated by Riggs, 

 that " the analyses do not represent ideal compounds. ..." 

 He therefore considers it necessary that further analyses of 

 more carefully selected material should be made. 



At about this time also Scharizer* published analyses of three 

 varieties of tourmaline from Schiittenhofen, Bohemia, and dis- 

 cussed his results in connection with the analyses of Riggs. 

 His final conclusion is that, with the exception of the green 

 varieties, tourmalines possess a chemical constitution which can 

 be expressed by the general formula 



[r,b],[b.K J .A].(SiO,) 11 [(BO, HO, F)J,. 



This formula is certainly difficult to comprehend, and, if we 

 understand it correctly, the univalent radicals BO and HO are 

 isomorphous with fluorine, and these constituents, taken twice, 

 can replace oxygen. 



In 1889 Jannasch and Kalbf published the results of nine 

 tourmaline analyses, in which the water and boron were deter- 

 mined directly. These investigators derived from their anal- 

 yses the general formula R 9 . B0 2 . (Si0 4 ) 2 , for which the fol- 

 lowing structural formula was proposed : 



I 

 () 



I 

 B = 



This formula, R 9 . B0 2 . (Si0 4 ) 2 , is identical with the one pro- 

 posed by Riggs, and essentially like the special formula 

 R^A^BSi^Oj,, of Rammelsberg. The following special formu- 

 las are also given : 



I. Li tour. 24Si0 2 . 6B 2 3 . 15 A1 2 3 . 4FeO . 4(Li 2 0, Na 2 0) . 7H 2 



II. Fe tour. 24Si0 4 . 6B fl O, . 14A1 3 3 . 9FeO . 2Na 2 . 7H 2 



III. Fe-Mg tour. 24Si0 2 . 6B 2 3 . 13Al 2 3 12MgO . 2Na 2 . 7H 2 



These special formulas in their general type are similar to 

 those proposed by Riggs. By substituting hydrogen atoms 

 for the metals they all reduce to one and the same acid, 

 H 1S0 B ]2 Si 24 O 126 or H 20 B 2 Si 4 O 2 , 



* Zeitschr. fur Kryst., xv, p. 343. 



f Berichte der deutschen chemischen G-esellschaft, vol. xxii, p. 216. Also In- 

 augural Dissertation, Geo. W. Kalb, Gottingen. 



