CERUSSITE CRYSTALS FROM BROKEN HILL AND MULDIVA. 



301 



Group VII (Plate LII, fig. 3).— This and Groups VIII 

 and IX are all portions of one large specimen, and they 

 naturally show some family resemblance; they beloug to 

 the reticulated type, the crystals being short in the direc- 

 tion of the vertical axis, tabular on b and elongated parallel 

 to the a axis. Group VII consists of seven individuals 

 twinned on wand r, the angular relations conforming fairly 

 well to the requirements of the two laws. Segment I, 5 cm. 

 long, is larger than the others, II and III are fairly large, 

 the others comparatively small ; there are a number of still 

 smaller individuals whose position could not be ascertained 

 and which have been omitted. The whole group is very 

 fragile and most of the terminations are wanting. The 

 commonest faces belong to the forms c (010), m (110), r (130), 

 fc (011); x (012), i (021), v (031), y (102), p (111) and w (211) 

 were also recognised. In spite of frequent striation the 

 signals were on the whole good and the orientation of the 

 crystals is well established. In the figure the crystals are 

 idealised but their relative dimensions and positions are 

 preserved. Segments which are parallel though not in 

 contact are numbered alike and the measurements obtained 

 from them are combined to find the mean angles given in 

 the subjoined table. 



Segment. 



v 



Limits. 



Number of 

 Observations. 



<f>o 



I 



206° 53 



206° 45 - 207 10 



11 



o / 







II 



329 32 



329 26 - 329 35 



7 



122 39 



III 



212 21 



212 13 - 212 35 



8 



5 28 



IV 



324 9 



323 59 - 324 14 



8 



117 16 



V 



269 29 



269 24 - 269 34 



4 



62 36 



VI 



274 56 



274 50 - 275 2 



3 



68 3 



VII 



332 4 



332 2 - 332 6 



3 



125 11 



The twins may now be readily recognised : — 

 Segments. Meas. b \ b 



I, II 57° 21' ) 



III, V 57 8 Calc. for f-twins 57 



VI, VII 57 8 ) 



8' 



