DALY. — ETCH-FIGURES ON AMPHIBOLES. 411 



Etch-Figures on the Clinopinacoid of Aluminous 

 Amphiboles. 



The cohesional properties of the plane (010) on any one of the akimi- 

 nous amphiboles are simpler than those of the same face on actinolite, in 

 that we find the development of only one kind of figure on the former 

 though etched in exactly the same fashion. It corresponds to the light 

 type on the actinolites in several respects, being a parallelogram with 

 the obtuse angle situated in the upper left hand corner and the non- 

 appearance of the adventitious third pair of figure-faces. The equiva- 

 lence is not complete because of the slight elongation in a vertical sense, 

 and because of a greater obliquity of the figure-faces to the plane (010). 

 (See Fig. 8 on page 406, and Plate I. Fig. 26, and Photograph 14.) 



We have seen that the pits on (110) of the hornblendes vary some- 

 what with the chemical composition ; the same is true of the (010) 

 pits. A number of specimens from different localities undoubtedly 

 with considerable, though unknown differences in the proportions of 

 the constituent oxides, were etched, and two of the elements determined 

 in each case, as recorded in the table : — 



There can be no question, in view of the facts of the foregoing table, 

 that there is a lack of uniformity in the crystallographic zones into 

 which the figure-faces on (010) of hornblendes fall. The differences in 

 outline and orientation are so salient as to impress the eye at once on 

 seeing them in the microscope. Now those hornblendes (V. 26, V. 33, 

 V. 34, V. 40, V. 54) which had the edge A B not far from being sen- 

 sibly perpendicular to the trace of the cleavage were also characterized 

 by (110) pits of the Wolfsberg sub-type, and those so far studied (V. 32, 

 V. 42, P. 55) that showed important variations from that orientation 

 carried pits more allied to the Kragero sub-type, if not identical with it. 

 More detailed investigation in the future with carefully analyzed material 



