,202 



NEW YORK STATE MUSEUM 



gave goniometer readings which corresponded to the indexes (2 12) 

 and (3-13). The letters 0— (2I2) and p — (3 13) have been as- 

 signed to these forms. The distribution of the occurring forms 

 is as follows : 



LETTER 



SYMBOL 













CRYSTAL 















1 



II 



III 



IV 



V 



VI 



VII 



VIII 



XX 



X 



XI 



XII 



a. . . . 



100 



010 

 310 

 210 

 320 

 110 

 230 

 350 

 120 

 130 

 111 

 111 

 212 

 313 



X 



X 

 X 



X 

 X 

 X 

 X 









X 

 X 

 X 

 X 







X 

 X 

 X 

 X 

 X 

 X 

 X 



X 



X 



X 



b 



X 

 X 

 X 

 X 

 X 



X 

 X 

 X 

 X 

 X 

 X 



X 

 X 

 X 

 X 

 X 



. . . 

 X 

 X 

 X 



X 

 X 

 X 

 X 

 X 



X 



z 



X 



a 



X 



X 





¥... 







f 



X 



X 



X 



X 



X 



X 



X 



2: 





d 









X" 

 X 















h 



k . . . . 



X 



X 





X 

 X 

 X 

 X 

 X 

 X 



X 

 X 

 X 

 X 

 X 



X 

 X 

 X 

 X 



X 

 X 

 X 

 X 

 X 



X 



X 

 X 

 X 

 X 



X 

 X 

 X 

 X 

 X 

 X 







1 



X 

 X 

 X 

 X 



X 

 X 

 X 



X 

 X 



X 



X 



X 

 X 



X 



n 







X 



P 



X 



X 



X 



X 



The following measured angles served to identify the forms ; the 

 theoretical angles are calculated from the elements given by 

 Beckenkamp 1 and adopted by Goldschmidt in his Krystallographische 

 Winkeltabellen. 



a :b:c = 0.4133 :i :o.6895 ^8 = 98° 58' 



Summary of measured and calculated angles 



■ LETTER 



ANGLE 



NUMBER OF 

 READINGS 



MEASURED 



CALCULATED 



b : a 



b : z 



b : a 



b : W 



101 : 100 

 101 : 310 

 101 : 210 

 101 : 320 



5 

 10 

 17 



5 



/ 



90 i 

 77 11 

 71 13 

 65 41 



/ 



90 

 77 12* 

 71 11* 

 65 35 



1 Zeitschr. f. Kryst. 1882. 6: 450. 



