144 BULLETIN OF THE UNIVERSITY OF WISCONSIN. 



Type 7. Another variety of the Galena marcasite crys- 

 tals resembles type 5 more closely, though s and m are 

 both very small. They are frequently attached by one of 

 the dome faces so that an opportunity is given for the de- 

 velopment of dome faces at both ends of the crystals. The 

 result is a mimicry of the octahedron, so that these crys- 

 tals might be taken for octahedral pyrite having small 

 truncations by the cube (plate 8, fig. 7). On some speci- 

 mens radial groupings of such crystals produce aggregates 

 having a diameter of about two centimeters, on which par- 

 ticularly large crystals or groups of crystals project at 

 points corresponding to the ends of the crystallographic 

 axes, and make the groups somewhat resemble hollow-faced 

 octahedrons. 



Dana' has figured a crystal from Galena which has a tab- 

 ular habit, is bounded by the forms I, v, c, b, m, e, and s, and 

 is twinned according to in. 



PYRITE FROM SHULLSBURG AND MINERAL POINT. 



Pyrite, like marcasite, is a common mineral in the crev- 

 ices of the Galena Limestone. Well crystallized specimens 

 would not, however, seem to be very common. During a 

 recent visit to the Wisconsin Zinc and Lead Company's 

 mine at Shullsburg, I picked up a specimen of limestone 

 having a small cavity lined with pyrite crystals. Some of 

 the individuals have a diameter of two to three millimeters, 

 but the better crystals are seldom much over a millimeter in 

 diameter. They are usually combinations of the common 

 pentagonal dodecahedron (210) with the cube and octahe- 

 dron, and are but little distorted. Their habit is gener- 

 ally conditioned by the pyritohedron, which is generously 

 truncated by the cube and octahedron (plate 8, fig. 8). In 

 a few cases the pyritohedron is but little developed, the 

 form of the crystals being given by the cube. The faces 



1 System, 6th Ed., p. 95, fig. 4. 



