438 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



TABLE I. — Continued. 



Of the observed forms thirty-six were previously known and twenty- 

 seven are new, seventeen of these being well established and ten requir- 

 ing confirmation. But five of the forms previously known for the 

 mineral were not present, namely, F, n, o>, y, and r. 



The combinations observed are shown in Table II. The prevailing 

 habit is strikingly hexagonal and of two types ; (1) tabular, with hex- 

 agonal outline (Figures 2 and 3), the prism angle m Am being 120° 28'; 

 (2) rhombohedral through the combination of a positive orthodome with 

 a negative pyramid of about the same inclination to the vertical, there 

 being three groups of forms that produce this effect, namely, w (101) 

 with v (122); u (201) with r (T21) ; and y (401) with R (211). 

 Figures 1 and 9 show the first pair of forms in pseudo-rhombohedral 

 combination. The apparent rhombohedral character is enhanced by 

 the fact that the angle (3 is very nearly 90°, so that the basal pinacoid, 



