102 Penfield and Foote — Composition of Tourmaline. 



There is evidence that Jannasch does not place great confi- 

 dence in the foregoing formulas, for in Hintze's Mineralogy* 

 the composition is expressed as follows : 



I. Lithia tourmaline Si 12 63 B 6 Al 15 (Na, Li) 4 H 7 

 II. Iron tourmaline Si 15 O fi7 iB Al" ,Fe q Na Q H, 



III. Magnesia tourmaline Si 13 69 B 6 Al 13 Mg ia Na 3 H 7 



These formulas are essentially different from the ones first pro- 

 posed, which may readily be seen by substituting hydrogen 

 atoms for the metals and comparing the resulting acids, as 

 follows : 



I. H 66 B 6 Si 12 63 or H 18f B 2 Si 4 0„ 

 II. H - B,8i lf O„ i or H 2S B s Si.,0^ 

 III. H 7J B 5 S ]2 6 , or H 24 B 2 Si 4 0„ 



Soon after the appearance of the articles of Riggs and of 

 Jannasch and Kalb, the results of their analyses were recalcu- 

 lated by Goldschmidt,f and the conclusion was reached that 

 tourmaline may be regarded as containing the two following 

 molecules : 



I. Alkali tourmaline R' 89 R"' 66 Si 91 1M 

 II. Magnesia tourmaline R' 20 R" 34 R'" 44 Si 81 O 1M 



These formulas are both derived from an acid H 200 Si 31 O 162 or 

 S 6 .«Si0 523 . 



In 1893 Rheineck,;}; after calculating the results of the many 

 tourmaline analyses, concluded that the composition of all 

 tourmalines may be expressed by formulas of the following 

 type, in which Al 4 appears as a constant : 



I. Alkali tourmaline Al 4 Si 3 BH 3 15 

 II. Alkali tourmaline Al 4 Si 3 B 2 H 4 17 

 III. Magnesia tourmaline Al 4 Si 5 B 2 M 4 H 4 2B , etc. 



M represents the bivalent metals Fe, Mn, Mg and Ca. H 

 includes Na, Li and IL Among the numerous examples he 

 stated that the composition of the black tourmaline from 

 Pierrepont, N. Y., may be represented by either of the follow- 

 ing expressions : 



< 114 Al.Si.B.M.H.O,. ( 10 Al.Si.B.H.O,. 



\ 10 Al.Si.B.0,. or \ 93 Al 4 Si,B,M 4 H 4 0,. 



I 21 Al 4 Si ( B 4 M 4 5B 



* Vol. ii, p. 311 (communication from manuscript by Jannasch). 

 f Zeitschr. fur Kryst , xvii, pp. 52 and 61. 

 X Zeitschr. fur Kryst., xxii, p. 52. 



