PALACHls.J 



Nczv Soda Amphibole, 



must be assumed that in it, .is in riebeckite, the axis o lies in the 

 obtuse angle of the crystallographic axes, and hence we have the 

 formula, b = B, c:o=ii°-I3° in front. 



The pleochroism is very strong; a, sky blue to dark blue; b, 

 reddish to purplish violet, very dark" in basal sections; r, yellowish 

 brown to greenish yellow, never colorless. Absorption formula, 

 y b > C, a and b being somewhat variable in the relative intensity 

 of their colors. These colors are in all cases more intense than are 

 those of typical glaucophane from various localities examined by 

 the writer. They approximate in intensity the pleochroic colors 

 of riebeckite. They are shown in Plate II, Figs. 2-9, as they appear 

 in the three principal sections of the mineral. 



Not infrequently the pleochroism reveals a zonal structure of 

 the amphibole in which the center of the crystal lias a lighter, more 

 greenish color, and a larger extinction angle than the rim. In a 

 clinopinacoidal section of a zoned crystal the outer portion was 

 found to extinguish at 12°, the inner greenish portion at 17 to the 

 cleavage. Plate I 1, Fig. 3, exhibits a basal section of such a zoned 

 crystal. This zonal structure is probably due to a local predomi- 

 nance or concentration of the actinolite molecule which, as will be 

 shown later, plays an important part in the composition of this 

 mineral. 



The blue amphibole frequently contains interpositions consisting 

 of grains of feldspar and sphene and minute zircon crystals. The 

 whole center of an amphibole crystal may be filled with feldspathic 

 matter (Fig. 2i~,) and the extremities of the crystals are frequently 

 frayed into brushes or fmgerdike projections, between which the 

 feldspathic matrix penetiates. 



A healing or enlargement of broken amphibole crystals by 

 secondary actinolite has been mentioned on a previous page. Such 

 crystals occur abundantly in sections which intersect any of the 

 veins which traverse the rock". The actinolite may either com- 

 pletely reunite the crystal fragments, as shown in Plate 11, Figs. 6 

 and 7, or it may project into the vein as a fringe on the broken 

 ends of the crystals, as shown in Plate 1 1, Figs. 1 and 8. It is rarely 

 or never seen on any portion except the ends of the amphibole 

 crystals. The actinolite is in exceedingly fine fibers, pale green in 



