252 



/:'. S. Larsm, -//•., and W. T. Schaller- 



one corner. The crystal laces are always dull and rough, .so 

 that accurate measurements were impossible. Several crystals, 

 however, could be measured with a contact goniometer and gave 

 for the angle r A r' the values: 91-0°, 91*3 , 91-2°, 91'7°, 

 average 91*3 or 91° 18'. The value of the c axis, computed 

 from this average angle, is 1/2677. Measurements of the angle 

 between the cleavage and the adjacent rhombohedron varied 



Fig. 1. 



Fig. 1. Basal section of hinsdalite. 



from 56° to 59°, with an average of 57° 18'. The calculated 

 value for the angle c A r is 55° 40'. 



The faces commonly developed on the larger crystals are the 

 unit rhombohedron r {1011} and the base c {0001}. The 

 smaller crystals are tabular, parallel to the base, and have both 

 the positive and negative rhombohedrons. The basal sections 

 are hexagonal, while the prismatic sections are lath-shaped, with 

 pointed ends. The optical properties show, however, that the 

 mineral is only pseudo-rhombohedral. 



The perfect basal cleavage gives wavy and striated surfaces, 

 and the. striations are in some cases developed in three direc- 

 tions, forming hexagonal markings. The hardness of hinsdal- 

 ite is about i 1/2 and the density is 3*65. The streak is col- 

 orless. The luster is vitreous to greasy. The crystals are nearly 



