364 Proceedings of the Royal Society of Victoria. 



Notes on the Remainder of the Mineral. 



1. Microscopic Investigation. — Included in the pyrolusite is 

 a colourless mineral generally occuring in aggregates of small 

 crystals. Occasionally a single crystal section can be found. 

 These sections are usuall}^ hexagonal in shape. One was 

 isotropic, and the angle between its sides was 120 deg., so that 

 the mineral would appear to belong to the hexagonal system. 

 The crystals are too small to give a satisfactory interference 

 figure with convergent polarised light. The refractive index is 

 high, and the interference colours yellows and greys. 



There is a third mineral present in minute quantities which 

 can be easily picked out by its red colour. It gives no very 

 satisfactory results in the slide, but can be obtained as separate 

 crystals by powdering some of the original specimen, damping 

 the powder, and then adding water. The red mineral is found 

 floating on the surface. It is evidently not wetted by the 

 water, and remains floating on account of the surface tension. 

 It may also be separated on account of being the last mineral 

 to dissolve on treating the powdered sample with concentrated 

 hydrochloric acid. Examined under the microscope, it is seen 

 to occur as well formed minute tabular crystals bounded by four 

 rectangular sides. Some crystals are pleochroic and doubly 

 refracting, and give a straight extinction. Others which are 

 not isotropic remain dark between the crossed nicols, and give 

 a uniaxial interference figure. The mineral is therefore 

 tetragonal. It may be wulfenite (PbMo04). 



Quartz also occurs throughout the pyi'olusite in rounded 

 grains of considerable size, which contain many liquid inclusione. 



2. Chemical Investigation. — A bulk analysis of the specimen 

 gave the following result: — 



Insoluble in concentrated rKaolin - - 4.14 



hydrochloric acid ^Quartz - - 5.22 



Soluble in concentrated 

 hydrochloric acid 



fMnO., - - 43.00 



PbO - - 25.96 



Al^Oa + FeA - 20.76 



Sb.A - - -30 



Cu - - - Trace 



99.38 



