FLANGED BUTTONS
Flanged buttons are the most famous australites,
yet the rarest! I have been lucky enough to find two fully flanged ones! - see My Flanged Button.
I have some flanged buttons for sale - buttons.htm
Many field collectors have found thousands of australites but not one fully
flanged one intact!
The word 'button' is often used to mean anything round or flanged and this can be
confusing. On this site I will only use the term 'button' in connection with complete
flanged round or oval forms. . All other types of australites with flanges will be called
'flanged' eg. a flanged teardrop, a flanged canoe, a flanged boat. Forms that have remains
of flanges will be described as 'part-flanged'.
The same features of ring waves can be found on any of the flanged forms but is rarely as
well developed as in the round and oval buttons.
Formation of a button
Only small primary forms developed
into flanged buttons. They rarely develop in forms over 6 gms in size. This is due
to the more rapid cooling in flight of smaller forms so that thin films of melt,
instead of being stripped away, move in waves to the outer rim of the primary body
where swirling back- eddies cause it to cool and solidify into a flange. At a
certain point the whole tektite solidifies preserving the pattern of the waves on the
anterior surface as they were on their way to the outer edge. Because of the very thin
attachment of the flange to the rest of the body, it rarely survives, often breaking away
in flight leaving the central lens to continue on to the ground, or it breaks away on
impact with the ground or in later erosion while on the ground.
Fully flanged buttons in good condition are quite rare.
Figures from the Shaw Collection:
Round buttons with perfect flanges
7
2.63 gms = 0.35% (of groupA-
unbroken australites)
Round buttons with half a flange remaining
22 2.
35 gms = 1.1%
Round buttons with less than half a flange
104
1.34 gms = 5.2%
Oval buttons with a perfect flange 2 2. 575 gms = 0. 1%
As can be seen, the fully flanged oval buttons are rarer than
round ones. If the percentage of the fully flanged buttons is taken for the entire
collection of unbroken and broken tektites, it comes to 0.2% which is two in every
thousand. This figure is actually quite high, there being a lot fewer in areas further
north.
The most perfect of all buttons have been found in the Port Cambell region of Victoria.
|
Round button from Rawlinna with bubble pit in centre. |
|
Other side of same button (anterior side) showing ring waves in a spiral pattern. (photos supplied by Guy Heinen) |
Flanges
It is extremely rare to find a complete flange ring which has
broken away from a button but fragments are often found.
|
Flange Fragments The fragments left show the diversity of flanges. |
The typical most common flange shows a 'rolled' effect which can
be seen if a cross section of the flange is made and viewed under a microscope. The
successive waves of melt were sufficiently hot and fluid to flow over the edge and roll
into the developing flange. A 'rolled' type flange is the most usual for tektites in the
3-8 gm range. Smaller tektites might develop a flatter, sharper, wider flange due to
the melt being more viscous. The melt was fluid enough to spread out but not to roll in on
itself. Smaller forms may have completely remelted and lost the original form of the
primary body and become nothing more than a thin, delicate 'flying flange'. In some of the
small forms with thin delicate flanges there has been a folding back of the edge probably
while still in flight. Some of these thin forms would have wobbled in flight creating
uneven flanges.
The precariously thin attachment to the button is the reason why fully flanged buttons
rarely survive and yet, going on the number of lens shapes found, they were probably the
dominant australite formed. The flange probably remained hot and molten in flight while
the centre remained solid and comparatively cool, creating a lot of stress on the very
fragile flange connection. Consequently most flanges would have become detached while
still in flight. If they did survive the flight then impact with the ground would have
broken off most of the others. Then if you imagine thousands of years of erosional forces
including animals and bush fires, it is a miracle that any at all have survived! To find a
complete unbroken flange ring is even rarer!
|
Left is button with wide flange.Central core is still slightly raised above level of outer flange. It is easy to see how it would eventually become a 'bowl' shape. - see below. |
Ring Waves
Also called flow ridges. These are the waves of melt which never
made it to the flange before the whole tektite solidified.
They are usually evenly spaced with average distance from crest to crest of 2 to 4 mm. On
the round buttons the rings can be spiral or concentric. Out of a sample of 75 australies
with well developed rings, 42 were in concentric circles, 15 had a clockwise spiral and 18
had an anticlockwise spiral. The spiral pattern could have developed due a slight
irregularity in the tektite such as a bubble pit.
Australites which are no longer flanged but show these rings would probably have been
flanged at some time including the huge number of lenses.
On some australites the flow ridges have been made irregular by the presence of bubble
pits. On others it seems as if the australite wobbled in flight and instead of forming
flanges, the waves of melt flowed around and over to the posterior side forming irregular
ridges on the posterior side. These are called 'crinkle tops'. Other irregular forms must
have changed direction during flight as they have flow ridges on both sides and some
dumbbells with one end heavier than the other have oriented with the heavier end forward
creating flow ridges down their length.
In many buttons the wave pattern becomes 'dimpled' and complex as it reaches the flange as
seen in the illustrations below of a flanged button and a flanged dumbbell.
 |
 |
Bubbles
These must have formed while the blob of glass was still molten and in the near vacuum of space. A volatile component within the blob has expanded while in space to form a low pressure bubble. We know this because a low gas pressure has been detected in unbroken bubbles. The bubbles have tended to migrate to the surface of the cooling blob and most have burst as the whole mass cooled leaving a neat pit on the surface. Most tektites have then oriented themselves aerodynamically with the centre of gravity as far forward as possible leaving the bubble pit on the posterior surface.