374 Tlic American Geologist. June, 1898 
formula as the probable one of the hornblende from Pavone, 
which would give us the following general formula. 
R^, R\' R7 Si^O,, 
or, writing monovalent elements as divalent ones, we get 
R" RTsi.o,, 
and consider jt as an orthosilicate. Scharizer* in 1884 in 
his article entitled "Die basaltische Hornblende von Jan 
Mayen nebst Bemerkungen iiber die Constitution der thon- 
erdehaltigen Amphibole," concluded that there was an or- 
thosilicate molecule with the formula (R^, R")^ (Al, Fe).^ 
Si.^0^2, which entered largely into the composition of cer- 
tain basic hornblendes. This molecule he called s}'ntagma- 
tite, using a name previously given by Breithaupt to certain 
hornblendes from Mt. Vesuvius or Monte Somma. The 
hornblende from Jan Ma)'en, the analysis of which is given 
above, coincides very nearly with the syntagmatite formula. 
Scharizer regards the aluminous amphiboles as composed of 
mixtures of the metasilicate molecule Ca (Mg, Fe).^ Si^Oj.^ 
(actinolite), and the orthosilicate molecule (R^, R")3 (Al, 
Fe)., Si.^Oj,, (syntagmatite). There is little reason why we 
should not accept this view, even as, in the feldspar and 
scapolite groups, we have accepted the theory that salts of 
different acids such as polysilicates and orthosilicates could 
form isomorphous mixtures with each other. The Pavone 
hornblende is an orthosilicate like syntagmatite but seems to 
have a more complex formula than the latter. We ma)' 
consider it as Syntagmatite plus a normal orthosilicate mole- 
cule, as follows: 
^^l R7 Si^O, e = "^l R^f 51.3 O, , + R\' SiO,. 
(Pavone hornblende) (Syntagmatite) 
In the past we have been too careless in making our horn- 
blende analyses, especially in the water determination, but 
this analysis of the Pavone hornblende as well as those of 
Scharizer, Berwerth and others makes it seem very probable 
that an orthosilicate molecule enters largely into the compo- 
sition of the aluminous amphiboles. 
*R. Scharizer, Neues Jahrbuch, 1884, II, 142. 
