MIXERALOGICAL NOTES — ANDERSON. 



85 



The calculated values of a and c agree fairly closely with 

 Koksharov's ratios a:b: c = 0^528542 : 1 : 0-476976, determined 

 on Russian topaz and usually taken as the standard. 



PL xix., fig. 1 is a stereographic projection showing the distribu- 

 tion of all faces that have been identified on Emmaville topaz. 



Oban, New South Wales. 



Mr. D. A. Porter recently presented to the Trustees a fine 

 large ciystal of topaz from Oban. It measures 4 cm. x 4 cm. 

 X 3 cm., and shows four forms not recognised on crystals from 

 this locality hitherto examined, namely c (001), d (201), h (203), 

 and X (043). It is shown in its natural development in PI. xviii., 

 fig. 2. The specimen is somewhat worn and the faces non- 

 retlecting, but approximate measurements obtained with the 

 contact goniometer leave no doubt as to the correctness of the 

 determinations. There is but one face of X present, but all the 

 others have the full number. One of the f (021) faces shows a 

 distinct natural etching-figure. It takes the form of a raised 

 semicircular area with its convexity directed towards the apex of 

 the crystal, the base of the semicircle being parallel to the inter- 

 section of f and c. 



Mount Cameron, Tasmania. 



Through the kindness of Mr. W. F. Petterd, a well-known 

 authority on the minerals of Tasmania, T liave been enabled to 



