12 FLANGES OF AUSTRALITES (TEKTITES) 
australite, the flange is broad, and carries few flow lines and one 
bubble-pit. ■ , i v.n 
On an oval, bowl-shaped australite figured by Baker (1940 a) 
a rare type of flange forms the sides and the small core the base 
of the bowl. In this specimen, probably a flat and thin flange was 
pushed backwards while plastic by atmospheric pressure. 
Internal Structures 
Internal structures of flanges and cores are intimately associated. 
They are best seen in thin plates, although distinct on weathered 
surfaces of fractured specimens and on artificially polished 
surfaces etched with a mixture of strong sulphuric and hydro- 
fluoric acids. In thin plates the Becke line effect clearly reveals 
the complexity of the flow patterns. 
After australit.es arrived at the earth’s surface, internal cracks 
(probably resulting from stresses set up during cooling) were 
infilled with ferruginous clay containing occasional grains of 
quartz (PL I, 2) ; similar material sometimes also infills the gap a 
and some bubble-pits. The cracks may traverse both flange and 
central core, sometimes cutting across the surface of union c 
from the gap a and bifurcating in the bas§. of the flange (PI. Ill, 
1 and 4). They cut across internal structures without offsetting 
them. 
The refractive indices of the flange glass of two australites from 
Port Campbell, of specific gravity 2 409 and 2 410, were found 
by the immersion method to be 1510 and between 1505 and 1510 
respectively. The glass is isotropic except for occasional bands 
of higher refractive index (1535) which sometimes exhibit strain 
polarization. Such bands are especially noticeable near the 
junction of flange and core and in contorted structures of flanges. 
Optical figures for these strained areas are too indefinite for 
accurate determination, although some appear to be biaxial. 
Strained areas are often colourless, the remainder of the glass 
being pale yellowish-green in thin plates except where colour 
banding imparts a deeper brownish colour (PI. II, 1 and 9). 
Inclusions 
The only inclusions in flanges and central cores are gas bubbles 
and minute glassy particles (Fig. 3). 
The bubbles are frequently circular, but may be elliptical along 
flow directions. All bubbles in flanges are minute, but in the 
central cores they may be larger and segmented (PI. I, 12) or 
