612 THE GEOLOGY OF TH K WARRUMBUNGLE MOUNTAINS, 



Remarks. — The curious patches of optically continuous felspar 

 noted above and the various stages of absorption exhibited by 

 the felspar of the tirst generation are matters which suggest that 

 this rock originated b}'^ the refusion of a previously existing 

 gabbro. Tlie fused mass then received an addition of alkaline 

 magmatic waters and a little alkaline lava. On the magma 

 reaching the surface man}'^ of the phenocrysts whicli had survived 

 the upward passage were now recrystallised. Tlie recrystallisa- 

 tion must have taken place after the lava came to rest, otherwise 

 the outlines of the crystals would have been lost. A kind of 

 hydato-igneous fusion must have taken place, otherwise we cannot 

 imagine how the magnetite was introduced, unless these crystals 

 were rich in inclusions to begin with. 



W.40. Loc: Billy King's Creek, 2 J- 3 miles south of Coona- 

 barabran. The rock forms a lava-flow. 



1. Handspecimen black in colour, consisting of a dark aphanitic 

 base containing a few felspar phenocrysts. 



2. Texture : the base is ver}'^ fine-grained, and has a trachytic 

 fabric. 



3. Constituents : the felspar phenocr3'^sts consist of albite; the 

 felspar of the base is mainly albite, but a little anorthoclase 

 appears to be present as well. A couple of perfectl}^ rounded 

 phenocrysts of andesine also occur. The next constituent in 

 order of abundance is a black dusty mineral, usually opaque, but 

 occasionally showing slight transiucency with a bluish tint. 

 ►Sometimes this mineral is seen in four-sided, five-sided, or six- 

 sided grains, but more often it is quite allotriomorphic, and 

 occasionally the dust occurs in groupings similar to the ophitic 

 groups of riebeckite in the trachytes. Most of it has a dull 

 lustre and is probably a variety of emery or corundum. A few 

 of the cubical grains consist of magnetite. It is possible that a 

 black, opaque garnet mineral may be present as well. The 

 felspar forms roughly 55-60 % of the bulk of the rock, the black 

 opaque minerals 10-15%. Next in order of abundance we have 

 a 3'ellow or brownish-yellow mineral in acicular prisms and 



