210 Washington — Kaersutite from Linosa and Greenland. 



rhonite (XII) is unique in its low silica, but in other respects 

 resembles our amplii boles more than it does the triclinic aenig- 

 matite, though the A1 2 3 is remarkably high. 



On the whole, therefore, our amphiboles may be considered 

 to belong to the basaltic hornblendes or syntagmatites, rather 

 than to the arfvedsonite group, and this general relationship 

 is confirmed by the color, the etch figures, and the negative 

 extinction angle of the Kaersut mineral. The very high Ti0 2 , 

 however, places them in a subdivision apart and, with the 

 small positive extinction angle of the Linosa mineral, indicates 

 a transition toward the arfvedsonite group. 



On account of their chemical characters, and also because of 

 the position of the negative extinction angles caC, barkevikite 

 (VII) and hastingsite (VIII) may also be regarded as transi- 

 tional between typical syntagmatite and the arfvedsonites, 

 though in the direction opposite to ours. A similar relation is 

 suggested by Brogger,* who regards kaersutite as an end 

 member of the basaltic hornblendes. 



The name kaersutite may well be reserved for such highly 

 titaniferous basaltic hornblendes or syntagmatites, and the 

 mineral from Greenland may be regarded as the type. 

 Whether the same name should be applied to the Linosa horn- 

 blende or not is somewhat doubtful. The two are chemically 

 closely similar, but show a marked divergence in the relative 

 amounts of the iron oxides. Also the physical characters are 

 alike in nearly all respects. The only differences of note are 

 the somewhat higher -specific gravity and indices of refraction 

 of the Linosa mineral, and the difference in the extinction 

 angle, which last would seem to be the more important. Indeed, 

 while that of the Kaersut amphibole is negative and lies well 

 within the limits of the extinction angles shown by the ordi- 

 nary syntagmatites, that of the Linosa amphibole is close to the 

 vertical axis, but slightly positive, and indeed occupies a unique 

 position between the extinctions of the riebeckite-arfvedsonite 

 group on the one hand and those of the syntagmatites on the 

 other, though it must be remembered that in the former group 

 the bisectrix which lies nearest the vertical axis is a, not c. 

 The physical characters of our two minerals are tabulated 

 below. 



The Linosa hornblende might be regarded as an end mem- 

 ber of the highly titaniferous syntagmatites, in which case the 

 name kaersutite would apply to it, or its peculiar extinction 

 angle, and the high ferric oxide might justify the separation of 

 it from this group as a distinct subspecies, to which the name 

 linosite may be given. In view of the uncertainty of our 



* Brogger, Grorudit-Tinguait Serie, p. 35, 1894. 





