140 BULLETIN OF THE UNIVERSITY OF WISCONSIN. 



cellent specimens from Mineral Point are included in the 

 University Collection. 



Type 2. On some specimens from the Linden Mine the 

 marcasite crystals have a lath- shaped habit due to their un- 

 usual development in the direction of the h axis, the macro- 

 pinacoid forming the edge of the lath, c the fairly broad 

 top, while the brachy domes at the top and bottom and m 

 from the vertical faces, produce a slight sharpening of the 

 laths at the ends (plate 8, fig. 2). All the faces are very 

 much curved and can not be measured. It is noticeable that 

 the prism is connected to the macropinacoid by a uniformly 

 curved surface. 



Type 3. This type of crystals is common on specimens 

 from Diamond Grove. The crystals are invariably stellate 

 twins, the individuals composing which have a thick tabu- 

 lar liabit w^ith c small and I large, and are but little striated 

 or rounded (plate 8, fig. 3). No simple twins were ob- 

 served, the groups being apparently cyclic fivelings though 

 the fifth individual is not made out owing to the broad at- 

 tachment of the twin by one of its edges. The reentrant 

 angles formed by m appear between individuals, but they 

 are very small. The face c is striated by oscillatory com- 

 bination with either I or i'. Unlike the crystals of type 1, 

 which have a brassy lustre, or those of type 2, which have 

 a greenish color, the surface of these individuals has a 

 reddish brown color and an iridescence which is ascribed 

 to incipient alteration to the hydrated oxide. The stellate 

 groups have a diameter of 3-4 ""'. and are attached to green- 

 ish marcasite which forms a surface layer over blende, its 

 tabular crystals being oriented normal to the surface of the 

 blende and crowded so closely that only the edges of I can 



be seen. 



Type Jf. This type represents the simplest combination, 

 the only forms developed being c and m (plate 8, fig, 4.). 

 The individuals are quite thick so that they have rather 

 the appearance of short prisms with diamond cross sec- 



