266 



RECORDS OF THE AUSTRALIAN MUSEUM. 



For chemical analysis some fragments were broken off, and, 

 after examination with a hand lens and removal of a slight iron 

 stain by liot hydrochloric acid, ground to fine powder. For 

 general analysis ■3241 gram was taken, for alkalies 4962 gram. 

 The alkalies were determined by Lawrence Smith's well-known 

 method, the amount of alkali in the calcium carbonate employed 

 being determined and allowed for. The filtrate from alumina 

 gave no precipitate with ammonium oxalate on prolonged 

 standing, hence lime, if present at all, must be in very small 

 amount ; other components possibly present in traces, as oxide of 

 iron, magnesia, and water, were not specially searched for in view 

 of the small quantity of material available. Further, the per- 

 centage of silica is slightly low and of alumina rather high, 

 perhaps owing to the contamination of alumina by traces of 

 silica not removed in the first operation. 



The appended analysis T. shows tliat the mineral is a nearly 

 pure potash felspar ; II. is Tschermak's analysis of adularia 

 from Pfitsch,^ while III. is the theoretical percentages for 

 KAl Si, 0,. 



Oban. 



(Plate xlviii., figs. 2, 3, 4 ; PL xlix., figs. 1,2; Pis. l.-lii.). 



In our collection there is a fine suite of felspar crystals, some 

 of large size, from this locality, a notable feature being the 

 excellent development of Baveno twins. This occurrence has 

 been noted by Porter when describing quartz from Oban,'-^ and he 



1 Tschermak— Ber. Ak. Wien, 1., (1), 1865, p. 577 (quoted Dana— Syst. 



Min., 6th edit., 1892, p. 319). 



2 Porter— Journ. Roy. Soc. N. S. Wales, xviii.,- 1884 (1885), p. 75. 



