Penfield and Foote — Composition of Tourmaline. 103 



By substituting hydrogen atoms for the metals in these ex- 

 pressions, and multiplying by the factors, 114 and 10 in the 

 one case, and 10, 93 and 21 in the other, the acids become 

 H 2866 B 28S Si 600 O 3100 and H MM B 190 S] 6M O i0il , or, when simplified, 

 H„. B 1 . 9 Si 4 O M . 6 and H I8 9 B 1 9 Si 4 O ao 8 . The improbable nature of 

 such acids is evident. In the opening paragraph of his article 

 Rheineck stated that the obscure and complex chemical rela- 

 tions of this mineral have necessitated a series of speculations 

 and calculations extending somewhat interruptedly over a 

 period of many years, in order to arrive at results such as those 

 embodied in the foregoing formulas. 



In 1895 Clarke* discussed the constitution of tourmaline and 

 proposed the following formulas : 



l. 2. 



/SiO = R'. /SiO -MgH 



Al— SiO = Al Al— SiO = MgH 



\Si0 4 =Al-B0 2 \Si0 4 =Al-B0 2 



I I 



Al-B0 3 = NaH Al_B0 3 =NaH 



/Si0 4 =Al-B0 2 /Si0 4 =Al-B0 2 



Al— SiO = Al Al— SiO ~ Al 



\SI0 4 ee Al \SiO = Al 



3. 4. 



/S10 4 ee M^H /SiO = MgH 



Al— SiO = MgH Al— Si0 4 ze MgH 



\Si0 4 =Al-B0 2 \Si0 4 = A1-B0 2 



Al-B0 3 =NaH Al-B0 3 =NaH 



/Si0 4 =Al-B0 2 /Si0 4 =Al-B0 2 



Al— SiO- MgH Al— SiO = MgH 



\SiO = Al \SiO = MgH 



Clarke assumes variations from these formulas in that Fe //; 

 and Cr can replace the Al ; Fe" and Mn the Mg ; Ca the 

 KaH ; and small amounts of F the B0 2 . Proof of a consti- 

 tution corresponding to the formulas cannot of course be 

 expected, but it is doubtful whether aluminium could exercise 

 such varied functions as the formulas indicate. The grounds 

 for believing that fluorine can replace B0 2 are not stated. The 

 acid from which all these formulas are derived is H 29 B 3 Si 6 31 

 or H lgi B 2 Si 4 2or 



Lastly Grothf has adopted the formula of Jannasch 

 [Si0 4 ] 2 . B0 3 . R',,, but interprets it as follows : 



* Bulletin of the U. S. Geological Survey, No. 125, p. 56. 



f Tabellarische Uebersicht der Mineralien, 4te Auflage, 1898, p. 11?. 



