ITALIAN PETROLOGICAL SKETCHES 563 



These characters made it seem probable that we have here a 

 growth of acmite about augite, as the last stage of pyroxenic 

 crystallization. Further examination, however, showed that the 

 bisectrix nearest the vertical axis is not a, as is acmite, but that 

 of least elasticity C- The greater number of crystals are cut 

 more or less nearly parallel to the vertical axis, but search 

 revealed a few cases of parallel growth where the augite and 

 the brown mineral were cut horizontally. In these the cleavage 

 cracks of the augite formed an angle of 88°, while those of the 

 external brown mineral formed angles of 122° with each other, 

 the planes b (010) and m (no) being present, and the direction 

 of least absorption being parallel to the clinopinacoid. The min- 

 eral is therefore an amphibole and may be referred to barkevi- 

 kite, with whose characters it closely agrees. It is regretted 

 that a chemical examination of this interesting mineral could 

 not be made, but the small amount of the substance and 

 its intimate association with the augite, rendered a mechanical 

 separation impossible. 



Bucca' mentions a brown pleochroic hornblende associated 

 with the augite of a leucite-tephrite (?) from Poggio Pilato 

 near Valentano, and also a similar amphibole in a leucite- 

 trachyte from Casaccia on Lake Vico.^ According to de 

 Stefani^ Rosenbusch observed a mineral like that described 

 above in the "basalt" of Radicofani. Rosenbusch'* also notes a 

 brown hornblende surrounding augite in an Ischian trachyte. 



It may be mentioned that since the chemical character 

 of the amphibole pointed to the pyroxene being a soda-rich 

 aegirine-augite, an examination was made to determine the char- 

 acter of the bisectrices of the latter. This showed that the 

 bisectrix nearest the vertical axis was C, so that it is an auo-ite 



to * 



Another leucite-tephrite from below Sta. Trinita near Orvieto 

 may be the same as that mentioned by Klein from this localit}-. 



■ Op. cit., 28. 



-BuccA, Boll. Com. Geol. Ital., 60, 1888. 

 3De Stefani, Boll. Com. Ital., 224, 1888. 

 ■» Rosenbusch, Mikr. Phys., II, 584, 1887. 



