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 1 has figured a crystal from Galena which has a tab- 

 ular habit, is bounded by the forms Z, v, c, &, m, e, and s, and 

 is twinned according to m. 



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 



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



