26 



S. L. Penfield — Pearceite^ a Suljpharsenite of 



The following angles were taken as fundamental : 



c Am, 001 A 110 = 90° 0' 

 niAm, 110 Alio = 60 2 

 c An, 001 A 101 =42 23 



from which the axial ratio was calculated 



a:b:c = l-YSOQ : 1 : 1-5796 

 y5 = 90° 0' 



The following table gives a record of the measurements which 

 were made mostly on one crystal. The ones in brackets repre- 

 sent approximate measurements from very narrow faces. 



Limits obtained 





Calculated. 



Measured. 





by Miers. 





c A m, 001 A 110 



90' 



' 0' 



90° 0'* 



90' 



' 4 









CA I, 001 A 310 



90 







90 



90 



2' 









mAm, 110 A 110 



60 



2 



60 2* 



60 







60° 



10'- 





c An, 001 A 101 



42 



23 



42 23* 



42 



23 



40 



48-42° 



30' 



c AZ/, 001 A 203 



31 



19 



31 22 













C A^°, 001 AlOl 



42 



23 



42 23 







> 







CA TT, 001 A 403 



50 



35 



50 44 













CAt°, 001 A 201 



61 



17 



61 25 







61 



8-61 



17 



CAO, 001 A 114 



24 



31 



(24 43) 













CAT, 001 A 112 



42 



22 



(42 43) 



(42 



9) 



40 



48-42 



30 



CAP, 001 A 111 



61 



16 



61 15 



(61 



V 



61 



5-61 



24 



CAS, 001 A 221 



74 



40 



(74 48) 







73 



55-75 



50 



CAU, 001 A 331 



79 



39 



(78 2) ? 













CAO°, 001 A 114 



24 



31 



(24 36) 













CAr°, 001 A 112 



42 



22 



42 24 













CAp°, 001 A 111 



61 



16 



(60 35) 













Up, 310 A 111 



40 



35i 



40 36 













^Ar°, 111 A112 



49 



26 



49 27 













r°A^°, I12A201 



49 



24i 



49 38 













t°AL 201 A 310 



40 



34 



40 34 













Certainly, as shown by the above table, the agreement be- 

 tween the measured and calculated values is very satisfactory, 

 and it may be assumed, therefore, that the axial ratio has been 

 determined with a fair degree of accuracy. That the crystal- 

 lization is really monoclinic is shown by the development and 

 arrangement of the faces, but the angle /9 differs so little from 

 90° that the variation, if any, falls within the errors of observa- 

 tion. Of four measurements that were made of c^l, the faces 

 being free from striations and giving excellent reflections, two 

 were 90° 0' and the others 90° 2^ Six independent measure- 

 ments of CA.m were made varying between 90° 0' and 90° 6\ 

 but the m faces were slightly striated so that the measurements 

 are not quite so reliable as those of Gy\l. 



delations of pearceite and polyhasite to each other and to 

 other minerals. — Pearceite and polybasite show, as would be 



