PROCEEDINGS OF SECTIOX C. 



449 



The mineral whicli occurs most frequently at Wodgina, and con- 

 stitutes almost the whole bulk of the ore exported, is manganotantalite. 

 A typical fragment from a large specimen of detrital ore from miscel- 

 laneous lease 86 was analysed with the results given in column A. 

 Those in column B were obtained from a single rhombic prism weighing 

 8 srrammes. . 



Tantalum pentoxide 68-65 



Niobium pentoxide 15'11 



Tintanium dioxide -40 



Tin dioxide -48 



Tvmgsten trioxide Trace 



Water combined -07 



Iron protoxide 1 -63 



Manganese protoxide 14* 15 



Nickel protoxide Trace 



Lime Trace 



Magnesia -15 



Cerium and Yttrium oxides . . Nil 



Total 100-64 



Specific gravity 7-03 



B 



69-95 



14-47 



•36 



2-68 

 (12-54) 



Nil 



100-00 



7-09 



This mineral is black on a fresh fracture with a metallic lustre. 

 Weathered surfaces are a rusty-brown color, due largely to a thin 

 adhering film of ferruginous clay. The masses, whether of lode or 

 detrital ore. frequently consist of an intergrown mass of parallel pris- 

 matic crystals, in which the faces a, b, and c are freely represented, 

 and, less commonly, u (133). These prismatic masses are inclined at 

 fimes to be wedge-shaped and, rarely, small masses are seen to be part 

 of a spherical " rosette " or radiated crystal group. The faces are 

 frequently indented by actual tabular crystals of albite, or by hollows 

 from which albite has evidently been weathered out. Twinning about the 

 plane e has been observed in several instances. The macropinacoid 

 a is often vertically striated, and at times has a very briUiant 

 lustre. In size the masses vary from many pounds in weight down to 

 a few grains only, and in the alluvial are often associated with tin ore, 

 though so far cassiterite has not been recorded from the veins which 

 carry tantalite. 



No normal iron tantalite has been observed at Wodgina, the whole 

 of the tantalite there being of the manganese variety. It is usually 

 of very uniform grade, containing from 65 per cent, to 70 per cent, of 

 tantalic oxide. Manganocolumbite has, however, recently been 

 obtained at Wodgina. This is identical with the richer ore, in all 

 physical features, with the exception of specific gravity which, as one 

 would expect, is correspondingly lower. Specimens of this mineral, 

 and of an ore of intermediate composition, gave the following results : — 



F2 



