Washington — Kaersulite from Linosa and Greenland. 207 



It might explain the inconsistency of the apparently greater 

 chemical complexity and hence probably greater molecular 

 weight Of the amphiboles, as suggested by Tschermak, and the 

 higher specific gravity of the pyroxenes, which Clarke* urges 

 as evidence of their greater molecular weight. It might also 

 readily explain the characteristic difference in pleochroism 

 between the two groups noted above. 



In this connection the analogy of the carbon compounds is 

 of interest. The greater part of these are referred, as is well 

 known, to two great groups ; the aliphatic compounds, deriv- 

 atives of methane, with an open chain type of formula ; and 

 the aromatic compounds, derivatives of benzene, with a closed 

 chain type of formula. These two groups show characteristic 

 differences in general chemical behavior, and also characteristic 

 differences in some physical properties. Thus, the aliphatic 

 compounds are very rarely colored, while colored compounds 

 are quite common among the aromatic bodies. Similarly 

 solutions of members of the first group seldom show absorp- 

 tion bands, while those of the other, when colorless, often do so. 



The analogy cannot, of course, be pushed very far, but that 

 such a fundamental difference in molecular structure would 

 not be inconsistent with the alteration of amphibole to pyrox- 

 ene, or the converse change of pyroxene to uralite, is indicated 

 by the convertibility of members of the aliphatic series into 

 those of the aromatic series, and vice versa. It may further- 

 more be observed that very many organic compounds are 

 known which contain radicals belonging to both series, such 

 as toluene (methyl-benzene), C 6 H 5 .CH 3 , and such pyroxenes 

 as aegirite-augite might be regarded as possible analogues. 



Correlation and Name. — In the annexed table are given 

 analyses of several hornblendes which resemble those of 

 Linosa and Kaersut in one feature or another. In their gen- 

 eral characters, on the whole, these most approach the basaltic 

 hornblendes, or syntagmatites, as Rosenbush has recently pro- 

 posed that these should be called, f especially in the figures for 

 silica, iron oxides, magnesia, lime, soda, and potash. The 

 alumina of our minerals is distinctly lower than in these, but 

 the figures for this constituent in analyses of the syntagmatites 

 (in this sense) are somewhat discordant. That shown in III 

 is very high, while the analyses of Schneider run rather 

 uniformly between about 14 and about 15. Also Ti0 2 is 

 much higher in I and II than in the syntagmatite analyses. 

 The analysis (III) of a typical " basaltic hornblende " shows 

 but little Ti0 2 , much less than in the analyses of Schneider (cf. 

 TV and YI), where it varies from 4*26 to 5*40. The correct- 



*F. W. Clarke, Bull. No. 125 U. S. Geol. Surv., p. 90, 1895. 

 fH. Kosenbusch, Mikr. Phys., vol. i, 2d half, 1905, p. 236. 



