6 



PBOOEEDINGS OP THE NATIONAL MUSEUM 



VOL. 72 



well suited for crystallographic measurement and the cause is not 

 entirely clear. The average values for <{> and p of the forms of rossite 

 are given in the following table : 



Table 6. — Averages of measured angles of rossite 



Form 



Number of 

 measurements 



« 



p 



a (100) 



14 



11 



5 



5 



/ 



85 38 



53 48 



72 54 



-86 38 



o / 



90 

 90 

 31 31 



44 13 



m, (110). 



c (001)... 



y (101) 





The value of the elements based on these measurements are as 

 follows : 



Table 7. — Axial elements of rossite 



Projection elements 



Polar elements 



Linear elements 



a;o'=0. 5829 

 i/o'= . 1906 

 Po'= .9730 



o / 



a;o=0. 4969 

 2/0= . 1624 

 Po= . 8295 

 90= 





t' = 85 38 



r = l 



o / 



o / 



h = 



X=80 39 

 M=59 31 



«'=85 38 



a=98 18 

 ^-97 24 

 7=89 34 



FORMS AND ANGLES 



Except for the forms h (010), a (100), m (110), c (001), and 

 y (lOl) no others were found except a few doubtful ones. These 

 doubtful forms were observed only once each and may represent, 

 in part at least, nothing more than the smooth surfaces by which the 

 crystals were attached to the walls of the crystallizing dish. All the 

 forms noted with the average angle of each are given in the table 



below : 



Table 8. — Measured forms of rossite 



Number 



Letter 



Number 

 of crys- 

 tals 



Number 

 of meas- 

 ure- 

 ments 



Symbol 



« 



p 



1 



2 



3 



4 



5 



6 



c 



b 



a 



m 



y 



15 



15 



15 



15 



5 



1 



1 



1 



15 

 30 

 30 

 30 

 5 



001 

 010 

 100 

 110 

 101 



72 54 

 00 

 85 38 

 53 48 

 -86 38 

 96 21 

 61 10 

 35 24 



31 31 

 90 00 

 90 00 

 90 00 

 44 13 

 64 00 

 44 00 

 88 23 



7 









8 

















