EXPLANATION OF PLATE 39. 



NEPTUNITE. 



Forms shown: c(001), a(100), m(110), s(lll), o(Tll), i(T12), 

 <7=(2ll), r(221), p (311). 



1. Common type. The form g is frequently slightly curved and is of 

 variable width, and p is often the largest of the terminal forms. The 

 back planes almost always cut much lower on the prisms than the front 

 planes. 



2. A not very common type with broad development of the unit pyra- 

 mids, s and o. It shows a common appearance of g with curved edges and 

 narrowing from center toward periphery. It is also very common for the 

 basal plane c to have this outline, elongated obliquely to the symmetry 

 plane, as is also shown in figures 3 and 4. 



3. From a doubly terminated crystal with peculiar geometrically 

 asymmetric development. It shows the two most common ways in which 

 r apjiears, depending on the development of g. 



4. Only one crystal of this type of develojMnent found. The front 

 pyramid ,s- cuts down lower on the prism than the back pyramid p; i and g 

 are absent, and r and /) occur as narrow strips bordering o. 



