214 Adams and Harrington — Alkali Hornblende and 



The Dungannon hornblende is interesting in connection with 

 the views of Scharizer, who suggested in 1884* that many of 

 the aluminous hornblendes might be regarded as molecular 

 compounds of the metasilicate actinolite, Ca (Mg,Fe) 3 Si 4 O ia , 



and the orthosilicate (R 2 R) 3 R 2 Si 3 12 , for which he employed 

 the name syntagmatite, originally given by Breithaupt to a 

 black hornblende from Vesuvius. The hornblende from the 

 Island of Jan Mayen, analyzed by Scharizer, f and that from 

 "Bohemia, analyzed by Schmidt,^: agree closely with the so-called 

 " syntagmatite molecule." The Stenzelberg mineral, analyzed 

 by Rammelsberg,§ also approximates to it ; but these three and 

 the Dungannon hornblende are the only ones yet examined, so 

 far as we are aware, that give at all closely the syntagmatite 

 ratios. The following table gives the analyses of these four 

 minerals and the molecular ratios deducible from them : 



In all four analyses the ratios for (R 2 0+RO) : R 2 3 

 (including Ti0 2 when present) are practically 3 : 1 : 3, 

 give the exact figures (excluding water) : 



:Sio 2 



or, to 



(R 2 + RO) 



Jan Mayen 2'87 



Bohemia 2*99 



Stenzelberg 3*14 



Dungannon 3*12 



R 2 3 

 I 

 1 

 1 

 1 



Si0 2 

 2-99 

 3'02 

 3-15 



3*07 



The ratio (R 2 0-{-CaO) : (Mg, Mn, Fe)0 is, as observed by 

 Scharizer in the case of the Jan Mayen and Bohemian horn- 

 blendes, approximately 3 : 4, thus : 



* N. Jahrb. f. 

 f loc. cit. 

 i Min. Mitth., 

 § Pogg. Ann. 



Mia., 1884, ii, p. 143. 



iv, 23, 1881. 

 185'8, -ciii, 454. 



