84 GEOLOGY OF MT. FLINDERS AND FASSIFERN DISTRICTS, Q., 



Fl.l. Log.: Stafford's Rock, near Mt. Flinders. 



Handspecimen : reddish-banded rock, aphanitic and showing- 

 flow-structure. 



Microscopic texture : microcrystalline phenocrysts are imbedded 

 in a microfelsitic (microaphanitic) base, partly isotropic and partly 

 birefringent. The texture is minutely hiatal-porphyritic and 

 micro-vitrophyric. The base predominates in amount (perpatic). 

 The phenocrysts are microlites of soda-rich sanidine. The clear^ 

 colourless, and birefringent constituents of the base likewise 

 consist of felspar, whereas the yellowish isotropic portion consists 

 of a mixture of crystallites, globulites and glass. A few minute- 

 tetragonal prisms and bipyramids with very high refractive index 

 and birefringence are present. They probably consist of zircon. 



Name : though rhyolitic in general appearance, no quartz is 

 visible,' so that we cannot say whether the rock is acid or inter- 

 mediate. It is best called '* hypohyaline zircon-bearing felsite '^ 

 allied to pantellarite. 



F1.2. Loc: Stafford's Rock. 



Handspecimen : whitish aphanitic rock with banded structure^. 

 A few megascopic felspar crystals occur in it. 



Texture — Crystallinity: hypocrystalline. Grain-size very fine- 

 and even-grained base in each band. Fabric : trachytic; and 

 porphyritic in microcrystalline phenocrysts immersed in a. 

 cryptocrystalline base. 



Composition : the phenocrysts are corroded prisms of sanidine. 

 The felspar of the base exists as microlites and crystallites. 

 Skeleton-crystals are common. The rest of the base consists 

 chiefly of isotropic material. The refractive index of the globu- 

 litic and glassy substance indicates the presence of much quartz. 

 A few red specks of limonite, black grains of magnetite and zircon 

 prisms occur. Some bands in this rock are coarser in grain-size 

 than others. 



Name : Trachytic Zircon-felsite, allied to Pantellarite. 



F1.4. Handspecimen : a dark greenish-black rock looking like 

 bottle-glass, which occurs as a flow underlying trachyte-felsite 



