116 Penfield and Foote — Composition of Tourmaline. 



indicate the general formula R 9 . B0 2 . 2Si0 4 , proposed by Jan- 

 nasch and Kalb. Their boric oxide determinations are in all 

 cases a trifle too low for the theory, but it is believed that the 

 reason for this is to be sought in imperfections of the method* 

 for determining this constituent in a complex silicate. The 

 analyses are excellent, and they rank with those of Riggs, 

 among the best analyses of tourmaline that have been made. 

 From our own experience, however, it is very questionable 

 whether tourmaline contains so much ferric iron as recorded 

 in some of these analyses (2*90 to 6*68 per cent). 



The analyses of Schakizer. — The ratios of the three 

 analyses are as follows : 







Total 



No. 



SiO a : B 2 3 



: hydrogen. 



65 



4 : 0-70 



: 20-9 



66 



4 : 0-76 



: 21-0 



67 



4 : 0-74 



: 20*2 



By comparing these ratios with the ones which have been pre- 

 viously considered, it would seem that there are good grounds 

 for believing that in these analyses the B 2 3 determinations are 

 too low, and that the bases have not been determined with 

 extreme accuracy. The ratios of Si0 2 to the total hydrogen 

 atoms in the main substantiate the formula H ao B a Si 4 O ai . 



Analyses from miscellaneous sources. — In looking over 

 the literature a number of analyses have been found which 

 need to be recorded. They have been made partly for the 

 purpose of identifying the mineral and partly for the purpose of 

 determining the character of the tourmaline from special 

 localities, but none of them have been made for the special 

 purpose of determining the chemical composition of the spe- 

 cies. It seems sufficient to give the ratios only, which are as 

 follows : 



Locality. Analyst. Si0 5 



69.fMt. Bischoft Sommerland 4 



70. Campolongo Engelmann _ 4 



7 1 . Sysersk, IJrals Cossa and Arzruni 4 



72. Montgomery Co., Md. Chatard 4 



73. Nevada Co., Cal Melville 4 



74. Tamaya, Chili ._. Schwarz 4 



75. Straschin, Bohemia ... Weisner 4 



76. Urulza, Siberia _ Stchusseff 4 



77. Kolar, India Chapman Jones.. 4 



Average 4 



* Bodewig, Zeitschr. fur Kryst., viii, p. 211, 1883. 



f 69, 70, 71 and 7 2 quoted in Dana's Mineralogy; 73, Bull. U. S. Geolog. Sur- 

 vey, No. 90, p. 39 ; 74, Zeitschr. deutsch. Geol. Gesell., xxxix, p. 238; 75, Min. u. 

 Petr. Mitth., ix, p. 410; 76, Zeitschr. Kryst., xx, p. 93; 77, Min. Mag., xi, p. 61. 





Total 



B 2 8 



hydrogen. 



0-98 



: 18-5 



0-82 



: 17-4 



0-89 : 



18-8 



0-84 ; 



! 20*4 







; 20-8 



1-02 ! 



• 19*1 



1-10 



: 19-4 



0-85 ! 



19-0 



0-87 



: 19-1 



0-92 



• 19-2 



