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



Augifce is next in importance, constituting perhaps 10 % of the 

 rock. It is of a light greenish, almost non-pleochroic variety, and 

 occurs in idiomorphic, but slightly corroded, square prisms. The 

 faces a (100), m (1 10), and c (001) appear to be well developed, and 

 h (010) not so well developed. The prismatic cleavage is poor, 

 but a marked cleavage parallel to a (100) exists in many crj^stals, 

 and a parting parallel to c occurs also. Extinction angle jC : c 

 about 45°. Optically +^®. A twinning parallel to a dome, pro- 

 bably (101), is well marked; contact twins, t\v. pi. a sometimes 

 occur, and a polysynthetic twinning parallel to a occurs in other 

 crystals. This kind of twinning may be due to decomposition, 

 for most of the augite is developing a hornblendic cleavage. 

 Zonal banding occurs. The properties determined point to an 

 augite lying between true augite and segirine-augite. The double 

 refraction is only 0*024, near that of diopside. Inclusions of a 

 yellow, feebly birefringent mineral occur as rounded masses in 

 the core of some augite crystals. The refractive index of these 

 inclusions is high. They may consist of a variety of allanite. 

 Magnetite occurs in fair amount (up to 5 %) as idiomorphic 

 grains. Apatite occurs as stunted rods and long needles pene- 

 trating both felspar and augite. Decomposition-products, such 

 as red-iron ores, chloritic staining, kaolin, etc., from alteration of 

 augite and felspar, occur in large amount. No nepheline seems 

 to be present. 



Name : Alkaline Augite- Andesite. 



Order of consolidation : 



1. Magnetite 



2. Apatite 



2. Augite (1st gen.) 



4. Felspar (1st gen.) 



5. Augite (2nd gen.) 



6. Felspar (2nd gen.) 



4. The Basalts. 



Basalts abound on the Darling Downs tableland, to the west 

 of the Little Liverpool Range. Basaltic eminences also occur 



