'//< Amph'ihol, iiinl Pyrowem groups. 



361 



bole cleavage and is unquestionably a member of this group. 

 The change to the blue amphibole may take place directly or 

 through the intermediate actinolite, while a change of the blue 

 into tne actinolite does not occur. The blue amphibole and the 

 the actinolite occur most prominently as enlargements of the 

 primary hornblende crystals, being added as a rule to the 

 clinopinacoidal or terminal planes. By means of the accom- 

 panying figures, drawn with the aid of the camera lucida, the 

 characteristic relationships will he most (dearly shown. 



Fig. 1 represents a cross section of brown hornblende of 

 entirely normal character. Upon the clinopinacoidal faces are 

 oriented additions of blue amphibole possessing a cleavage 

 plainly parallel to that of the brown, and to the boundaries of 

 the new growth. The two minerals are sharply defined by their 

 pleochroism, being of very nearly the same pale yellow color 

 parallel to the shorter diagonal of the prism, while the one is 

 brown and the other a deep bine parallel to the longer diago- 

 nal* 



In tie;. 2 is given a section nearly parallel to the clinopina- 

 coid of a hornblende crystal with the blue amphibole added in 

 liame-like forms upon the terminal planes. These two figures 

 give the characteristic outlines assumed by the added blue 

 amphibole in nearly all cases. The delicacy of the termina- 



4. 



tions of the growths i> not accurately represented by figure 2, 

 for the ends of the spires are often made up of tufts of needles 

 not perfectly orientated and blue fibers are attached to the 



* In all figures of this article the stippled portion represents brown hornblende; 

 the stippled with black lines, blue amphibole or allied forms; with white lines, 

 augite; and the white arras, actinolite, unless otherwise Btated. 



