144 VOLCANIC AREA OF EAST MORETON, ETC., DISTRICTS, Q., 



In Ngun-Ngun pantellarite, grains of an amphibole with a 

 reddish to brown to bluish pleochroism occasionally are seen as a 

 nucleus of a crystal of arfvedsonite. These may be a variety of 

 cossyrite or katoforite. The grains are too rare and minute for 

 determination. 



The blue hornblendes in minute rods and dendritic (poikilitic, 

 pegmatitic) aggregates were too small for exact determination. 



Cossyrite is far more plentifully distributed in the East 

 Moreton and Wide Bay trachytes than I formerly supposed. It 

 is an abundant minor constituent in the rocks of Ngun-Ngun, 

 Trachyte Range, Beerburrum, Cooran and Coolum. It has a 

 cleavage angle of 66°, is of a deep brown colour and pleochroic, 

 from opaque brown to yellowish-brown. A variety in the Ngun- 

 Ngun trachyte has a purple pleochroism in certain positions. 

 The occurrence of cossyrite and barkevicite in the trachytes 

 shows that titanium was present in the magma. Sphene occurs 

 in the Ngun-Ngun rock in small dendritic prismatic aggregates. 

 In this rock cossyrite occurs both in crystals and as poikilitic 

 aggregates, the latter of which is its usual habit in the other 

 trachytes. 



Associated with the hornblendes in most of the trachytes 

 under discussion we have segirine. This pyroxene occurs in 

 acicular and lath-shaped crystals of a green colour, which exhibit 

 strong pleochroism, from brownish-green to bright sea-green to 

 yellowish-green, and much higher double refraction than the. 

 amphiboles. ^Egirine is the main ferromagnesian mineral in 

 the rock types from Mt. Ewin, Trachyte Range (Skeleton Cave),. 

 The Round Mtn., and part of Conowrin. In the Conowrin rock 

 it is always associated with riebeckite. In the other trachytes 

 aegirine is present in much smaller quantity than the hornblende. 

 Quartz is a common constituent in some of these rocks. Mt. 

 Cooee comendite contains corroded quartz phenocrysts; in the 

 Ngun-Ngun and Conowrin rocks it is occasionally seen in the 

 base, forming a micrographic or cryptographic (pseudospherulitic) 

 intergrowth with orthoclase. In Coolum comendite spherulites. 

 of quartz (chalcedony 1) and felspar (sanidine) occur. 



