148 



BULLETIN OF THE UNIVERSITY OF WISCONSIN. 



113 30 



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, ao Poo (100) ; 

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

 being very small and recognized only when the crystal is 



