876 THE GEOLOGY OF THE NANDEWAR MOUNTAINS, 



N.59 B is a rock in which nuclei of dark arfvedsonite or 

 riebeckite of a deep blue-black colour are surrounded by a lighter- 

 coloured arfvedsonite or segirine, sometimes the one, sometimes 

 the other. The dark arfvedsonite is like that of N 46; segirine 

 is the dominant ferric mineral. The light-coloured variety of 

 arfvedsonite, however, displays peculiar properties. Bx^ = a, 

 hence it is negative, and the absorption is 



C (bright greenish-blue .> b (lavender) .> a (greenish-yellow). 

 Possibly this mineral may be an aberrant variety of segirite. 



Pyroxene, varies from pure segirine to segirine-augite. It 

 answers to descriptions given of the same mineral in the 

 Warrumbungle Petrology. 



(b) Minerals sparingly represented. — Many of these are 

 represented only by grains of such minute size that it has not 

 been found possible to make an exhaustive examination of 

 optical properties. 



Cossy7'ite(l) occurs very sparingly and is recognised in sections 

 where it occurs in extremely fine-grained poikilitic aggregates, by 

 its deep brown colour, strong pleochroism and cleavage angle of 

 65^. 



Katophorite (?) occurs in dendritic aggregates of somewhat 

 acicular crystals often surrounded by haematite or a zone of 

 arfvedsonite and segirite. This mineral is strongly pleochroic in 

 colours of deep purple, red, fine deep red, brown, yellow, and 

 gieenish-yellow. There are apparently several varieties graduat- 

 ing into arfvedsonite, cossyrite and ferrite. This mineral com- 

 monly forms only the kernel of crystals of pegirite and arfved- 

 sonite. It appears to me for this reason that the arfvedsonite 

 and segirite are products of pneumatolysis commencing after the 

 brown hornblendes had commenced to form. This vapour-action 

 often completely decomposed the original katophorite, leaving 

 ferric oxite (ferrite) in its place, and the NaoO, SiOg, TiOg, etc., 

 of the molecule were redistributed amongst other minerals of the 

 rock. Only in this way can I explain that we often meet with 



