162 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



to such a degree as to give a pointed trigonal or pyamidal termination. 

 Many crystals were measured and a very complex form series was found 

 to be present, full details of which are to be found elsewhere. ^^ jt may 

 suffice to state here that parisite was found to be undoubtedly rhom- 

 bohedral in symmetry and to be referable to axes having the ratio 

 = 1 : 1.2912. The forms of most prominent occurrence are the 



a 



base and second-order prism, c(OOOl), a(ll20), 



Figure 6. 



Figure 7. 



second-order pyramids, (ll53), (5.5.TU.12), (44H9), r(22i3), (4453), 

 positive rhombohedrons, (4.0.1.15), (20^5), (50o4), k(202l), s(3o5l), 



(10.0.T0.3), (50ol), (60^1), 

 negative rhombohedrons, (0.3.3.10), (0.9.^.25), (022l), (0552), (0331), 



(04il), (06^1), 

 scalenohedron (4.2.1^.11), 



Figures 5, 6, and 7 show typical combinations. 



The relation of the position here adopted for the crystals of parisite 

 to" that formerly used (as in Dana, System, p. 290) maybe stated thus : 

 the former second-order pyramid series corresponds to the rhombohe- 

 drons of the new position; the former unit pyramid p(loTl) receives 

 the new symbol p(ll2l), the former second-order pyramid g(ll23) 

 becomes the new positive unit rhombohedron g(lOTl). 



Optical Properties of Parisite. — As seen under the microscope, very 

 small crystals or fragments are a very pale yellow to almost colorless 

 and show a barely perceptible dichroism. For crystals \ mm. thick the 



" Am. J. Sci., 31, 533 (1911). Zeitschr. fiir Kryst., 49 (1911). 



