316 Penfield — Crystallography of GoBsium-Meroury llalldes. 



«, 100, i-% m, 110, / 



&, 010, i-i n, 130, i-3 



Measured.. Calculated. ' 

 m a m, 110 a 110 = *60° 0' 

 d a<7, 021 a 021 =*101 274 

 p aJ, 111 a 111 = 66 234 66° 29' 

 p A_p, 111 ~ 111 = 36 54 36 54 

 m~p, 110 ^ 111 = 50 43^ 50 43£ 



e, 101. 1-7 



f. 20 1, 2-1 



./. 021, 2-1 

 p, 111, 1 



Measured. Calculated. 



a *p. 100 ^ 111 =56 c 45' 56° 45+' 

 m *p. 110^111 = 71 334, 71 33" 

 p ~d, HI a 021 = 36 54 36 54 



a ~e, 100 ~ 101 = 54 424 54 42 

 a a/, 100^201 = 35 13 35 134 



The crystals were brilliant arid gave wonderful reflections. 

 The prismatic angle was measured repeatedly and found to 

 be 60° and the forms could be referred to the hexagonal sys- 

 tem, making the m and b faces a prism of the first order, a 

 and n a prism of the second order and p and d the unit pyra- 

 mid. There was nothing, however, in the development of the 

 faces to suggest hexagonal symmetry. Thin sections were 

 prepared, hoping that the optical proj)erties would throw some 

 light upon the form, but they showed only a very weak 

 double refraction, in fact they appeared almost like isotropic 

 sections, so that no satisfactory conclusions could be drawn. 



The crystals of the second type were spear-head shaped, fig. 

 17, and grew out into the center of the solution, either attached 

 to one another by the acute solid angles, or to a slender, paral- 

 lel growth of crystals, which served as a sort of stem. The 

 crystals which are about 5 mm in length are complicated and per- 

 plexing, and the faces are developed with triclinic symmetry, 

 although they can be referred to the axes of the first type. 

 The most prominent faces are shown in the figure, while the 

 distribution of all those which gave distinct reflections are 

 given in the spherical projection, fig. 18. The forms which 

 were observed are given as if they belonged to a triclinic crys- 

 tal and are : 



17. 



18. 



19. 



'10. 



i, 010. i-i 

 to', 110, 'I 

 /, 201, '2-1' 

 d, 021. 2-1' 



p, 111, I' 



P', lib ,1 



P", 111, 1, 



Q. 132, |-3' 



', 132, '|-3 

 131, ,3-3 

 191, ,9-9 

 1151, .15-15 



z", 197, f-9^ 

 v, 1131, 11-^' 



