90 E. S. Dana — Chondrodite from the Tilly-Foster Iron Mine. 



Taijle XIII. 

 Chondrodite. 



these angles a little uncertain. The macrodomes in one case gave 

 good measurements; and making use of the best of them, C/\i^{l-i) 

 r=144° 47', and also the same prism as in type II, after the analogy 

 of humite, the angles were calculated throughout. It was found, 

 however, that wherever trustworthy they corresponded so closely to 

 what was required to satisfy the ratio of 10:9 for the vertical axes 

 (asserted as approximately true by Scacchi, i. e., 5 : 9 for his axes, and 

 finally proved rigidly by vom Ratli), that the calculations were made 

 on this supposition. The calculated angles, as now given, conse- 

 quently have as their basis the prismatic angle Iy,,I=z94° 44' 14" and 

 the macrodome angle C^i'=l^-i° 45' 11 ". 

 The coiTcsponding parameters are : 



a (vert.) = 1-41512; b = I ; c = TOSBSO. 



