FLANGES OF AUSTRALITES (TEKTITES) 17 
Specific Gravity and Composition 
The specific gravities of 107 flange fragments and three 
complete detached flanges from Port Campbell range from 2 31 
to 2 44, the average being 2 '385; the average for cores is 2 '426, 
range 2 34 to 2 49 (Baker and Forster, 1943). The difference 
in the mean values, 0 04, suggests that flanges are more acidic 
than central cores, since the specific gravities of australites rise 
as their silica content decreases. This is borne out by specific 
gravity determinations of the powders of flange and core of two 
australites from Port Campbell; the specific gravity of the core 
of a boat-shaped specimen is 2 34, that of its flange is 2 29; for 
a button-shaped specimen, the specific gravity of the core is 2 '33, 
that of its flange 2 '29. 
Variation in composition within some flanges is also indicated 
by colour banding and by differences in refractive index. Bands 
coloured deep brown in thin sections are evidently richer in iron 
than the surrounding pale green glass. 
Origin of Shapes and Structures 
According to Dunn’s bubble hypothesis (1912 b), the glass of 
australites flowed downwards from the top (posterior) towards 
the bottom (anterior) surface. It is now, however, generally 
accepted that the movement of molten glass was from the anterior 
surface towards the equatorial region (Fenner, 1934). 
Dunn thought that the flanges were not sufficiently hot to 
coalesce with the cores along the junction c (Fig. 1). In some 
instances, they must, however, have been sufficiently hot because 
(a) some bubble-pits on the posterior surface of the core have 
been re-enclosed by the glass of the flange, and (b) in “crinkly- 
top” types (Fenner, 1934) melted glass spread over portions of 
posterior surfaces. In general, the material of the flange solidified 
before coming into complete contact with the glass of posterior 
surfaces of cores, leaving the gap a (Fig. 1). 
According to the hypothis of meteoric origin, the front surface 
in australites was melted by heat generated by friction of the air 
(note by Suess, in Fenner, 1935) or was already molten when 
shed from a burning light-metal meteorite. Under pressure by 
the atmosphere this molten glass flowed towards the equatorial 
region and formed the flange ; some molten glass was lost during 
flight, however, as evidenced by truncated flow lines in the flow 
troughs. The congealing glass of the flange was forced back by 
pressure and frictional drag, and was partially rolled in upon 
