MINEKA LOGICAL XOIES — ANDERSON. 93 



CERUSSITE. 



At the Magnet Mine, Tasmania, cerussite occurs in two different 

 habits, long prismatic or tabuhir on the h (010) pinacoirl (PI. xx., 

 fig. 1), and as fiat tal)les parallel to the basal plane (PI. xx., 

 fig. 2). In both cases the crystals are twinned on the faces m 

 (110) and m'" (110) resulting in trillings of pseudo-hexagonal 

 form. A specimen in the Museum collection furnished ciystals of 

 the first habit, while Mr. W. F. Petterd obligingly lent some 

 examples of the other. An interesting feature is that the flat 

 pseudo-hexagonal tables of the second habit are invariably con- 

 taminated with chromate of lead, doubtless in the form of croco- 

 isite, which imparts to them a canary-yellow colour with occasional 

 patches of red. The occurrence is well d,escribed by Mr. Petterd.^" 



" This attractive variety [habit ii.] of a common species 

 is, so far as known, confined to the Magnet Mine, in the upper 

 workings of which it is, although local, fairly abundant. It 

 occurs in fractures and vughs in the gossan zone, but in bunches 

 and sparsely attached as beautiful little crystals, generally in 

 close association with crocoisite, but never so far as observation 

 has gone intermixed with the normal form [of cerussite] ; 

 although this is somewhat abundant in its usual adamantine 

 characteristic habit, often showing remarkably perfect develop- 

 ment in stellar and cruciform triplet crystals." 



Habit I. (PI. XX., fig. 1.) The two crystals measured were 

 essentially similar, being elongated along the vertical axis and 

 tabular on the h (010) pinacoid. The same forms are present in 

 both, namely c (001), a (100), b (010), m (110), r (130), i (021), 

 x- (102), and ^^ (111). In the figure the breadth along the a axis 

 is somewhat exaggerated, and the three individuals are drawn in 

 equi-poise, though really only one is well-formed, the other two 

 being quite subordinate. All the forms except b are relatively 

 narrow and the prism zone is much striated and interrupted. 

 Of the three individuals forming the trilling, I. is placed in the 

 conventional position, while II. and III. are twinned on the faces 

 (110) and (llO), respectively, of I. Thus the faces ?m and ^are 

 coplanar ^vith m and p, while m and p are coplanar with m ' ' ' 

 and p" ', and similarly at the other end of the a axis of I. but II. 

 and III. have only one coplanar face, namely, the Ijase c. The 

 figure is similar to the well-known drawing by Schrauf^', but the 



10 Petterd— Kept. Secy. Mines Tas., 1903 (1904),'pp. 76-77. 

 " Schrauf— Tscherraak's Mineral. Mittheil., 1873, Heft iii.. pp. 203-212, 

 PI. iii., fig. 2. 



