O PROCEEDINGS OF THE NATIONAL MUSEUM. vol.63. 



133 (^1). A form not previously recorded, although there are 

 listed in Goldschmidt's Winkeltabellen two forms, (13.39.40) and 

 (3.9.10), which are very close to it. The new form was observed as 

 three faces — two on crystal 1, shown in Figure 1, and one on crystal 

 2, shown in Figure 2. Angles: 



Measured, crystal 1 <t>=2S 03 p=37 45 — poor. 



Measured, crystal <>=27 44 p=37 43 — poor. 



Measured, crystal 2 <;!>=27 54 p=37 47 — very good. 



Calculated, 133 0=27 55 p=37 42 



Calculated, 13.39.40 <^=27 55 p=37 05 



Calculated, 3.9.10 <t>=27 55 p=34 54 



The form is thus well established. 



Fig. 4.— Polyba.site Crystal Showing Actual Development. 



3.10.5 (f 2). This form is represented by a single relatively 

 prominent face yielding a good signal on crystal 3, as shown in 

 Figure 3. Angles: 



Measured <^=25 37 p=57 37 



Calculated 0=25 30 p=56 37 



Difference <!>= 07 p= 1 00 



The polybasite crystals are black in color and very lustrous. The 

 best crystal was measured and is faithfully reproduced in the drawing 

 Figure 4. Oriented as drawn, the angles are in very close agreement 

 with those given in the Winkeltabellen. The crystals do not exhibit 

 any unusual features, the habit being .tabular, as is characteristic 

 of the mineral. They show the usual step structure, as indicated 

 in the drawing, this tendency being manifested also in hexagonal or 

 triangular markings on the basal pinacoid. The streak of the poly- 

 basite is dark red, and, in the absence of distinct crystals, it might 

 be mistaken for pyrargyrite. 



