148 



BULLETIN OF THE UNIVERSITY OF WISCONSIN. 



Measured. 



46 12' 



88 5 



44 23 



22 44 



22 21 



35 45 



26 42 



43 15 



98 3 



53 21 



58 4 



40 35 



113 30 



Calculated. 



47 12' 

 87 37 

 44 44 



22 49 



22 53 

 35 21 



27 52 

 42 50 



99 48 



53 6 

 59 12 



113 6 



The crystals are translucent with the beautiful azure 

 blue color characteristic of this mineral. They are some- 

 times coated with a thin film of green malachite. 



MALACHITE FROM MINERAL POINT. 



This mineral is found as a superficial alteration product of 

 chalcopyrite. Some very beautiful radial and sheaf-like 

 forms are to be seen in specimens in the University Collec- 

 tion. Some very minute crystals having a maximum length 

 of only about three-tenths of a millimeter, when examined 

 under low powers of the microscope appear as columnar 

 crystals much flattened in the plane of the ortho-pinacoid 

 (plate 7, fig. 5). This face is so much broader than the 

 others that the crystals invariably rest upon it and conse- 

 quently always exhibit parallel extinction. They are in all 

 cases bounded very sharply by the forms a, ooPoo (100); 

 m, ooP (110); c, OP (001); and 6, ooPoo (010); the latter plane 

 being very small and recognized only when the crystal is 



