BY W. F. PETTERD, C.M.Z.S. 43 



plane, and in being greatly shortened along the vertical 

 axis, the result being flat tables approaching the hexagonal 

 forms. That they are trillings is at once apparent from 

 the re-entrant angles on the edges, and the three systems 

 of striations on the basal plane, which are well seen under 

 the microscope, crossing at angles of approximately 60° 

 and running parallel to the brachy-axis of each individual. 

 Crystals of a similar habit have already been observed in 

 aragonite, but prismatic crystals seem more common with 

 cerussite. One lot of isolated crystals of a pronounced 

 yellowish colour average 6 mm. in diameter. A few 

 smaller crystals measuring about 1 mm. in diameter, 

 translucent, and of a much paler colour, were found 

 implanted on the matrix. These latter supplied the best 

 measurements on the goniometer. The most prominent 

 face after the basal plane is the pyramid o (112); only 

 one doubtful angle could be referred to the prism r, which 

 is accordinglv not entered in the figure. The forms recog- 

 nised are c (001), a (100), b (010) m (110), / (021), k (Oil) 

 p (111,^ o (112). The drawing suggests Laspeyre's figure 

 of aragonite Irom Oberstein ; only our crystal has more 

 forms, and is drawn in ideal symmetry. The measured 

 agree well with the theoretical angles." 



Analysis of the characteristic form of a yellowish-green 

 colour from the Adelaide Proprietary Mine, Dundas, by 

 Mr. J. C. H. Mingaye, F.C.S., of Sydney, N.S.W.: — 



Pb O = 83-07 per cent. 



C O., = 15-97 „ 



C/^ Oj = minute trace 



Gangue = -62 per cent. 



99-66 



Variety — Chromiferous Cerussite (Lead Carbonate 

 with Chromic Acid). 



This attractive variety 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, 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; although this is somewhat abundant in its usual 

 adamantine characteristic habit, often showing reniark- 

 ably perfect development in stellar and cruciform triplet 

 crystals. 



