Surface Texturing On Tektites Ė Part-2
In this monthís article on tektites we will continue on with last monthís discussion on the surface texturing of tektites. This month we will look at the grooved Philippinites, a Billitonite, and the flanged Australites. These are all specimens from the Australasian Strewn Field. The four specimens below are all large Philippinite spheres. Please click on the thumbnails below to view in more detail.
The first specimen shows just the beginnings of the grooves starting to form. The next three specimens show a progression of groove formation. In 1923, Van der Veen carried on an experiment whereby he removed all external surface texturing on a group of specimens. He then heated the tektite and then cooled them in a water jet. He discovered that cracks formed on the outer surface of the specimens. Van der Veen then exposed the tektite to HF (hydrofluoric acid). He then discovered that the attack of the HF on the specimen followed the cracks that had developed by the heating and cooling process producing grooves that are very close in appearance to the meandrine grooves which appear on some Billitonites. The grooves formed were also similar in that they had the characteristic "U" shape in a cross section. Below is an excellent Billitonite specimen showing both sides of the specimen. The right image shows the meandrine grooves.
It is interesting to note that the meandrine "U" shaped groves only appear on half of this sphere. The oblong specimen we used to have in our possession also had the grooves on only one side. This trait can also be seen on the Billitonite on page 64 of O'keef, J. A., 1976, Tektites And Their Origin. We suspect that the side with the grooves is the anterior side which experienced more thermal shock during it's flight.
The flanged Australites are the most fascinating of the tektites and their surface features are the best understood. A glob of plastic tektite glass solidifies as a solid sphere before itís re-entry through the atmosphere on it's impact fate with Earth. During itís re-entry, atmospheric friction melts the anterior side which flows back toward the posterior side of the sphere forming a flange. Below is a thin section made and photographed by Jim Tobin. You can clearly see how the melt rolls up to the posterior side of the sphere and forms the flange. If you look closely below the flange towards the anterior side you can see the bumps of 3 ring waves.
The two flanged buttons below show specimens in both pristine and weathered condition. The specimen on the left exhibits surface texturing on the original sphere portion which is not seen on the flange. This texture on the sphere is often found beneath the flanged area indicating that these markings are created during the formation process and not a re-entry marking. It would be interesting to cut and examine the specimen on the right to see what the original surface condition of the sphere is under the flange compared with the surface texturing we see below. We will not of course be cutting a perfect chip free flanged button.
The two images below are the anterior side of the upper left specimen. The left image shows wonderfully detailed concentric ring waves formed during re-entry. The image on the right shows what appears at first glance to be a crack and chipped area due to it's impact with the surface of the Earth.
Upon closer examination we see that the ring waves around the defect area are not the even concentric lines as seen in the upper left image, but instead show that the defect has caused turbulence in the airflow which caused a deformation in the ring wave structure. This shows that this specimen must have had an impact during it's re-entry phase and not due to ground impact. This impact created the crack and surface damage as seen below. The impact was severe enough to cause damage but not enough to destabilize the specimen during the remaining re-entry. If the impact had caused the specimen to start tumbling you would not have the deformed ring waves on one side and perfect ring waves on the other.
Below is a close up of the damages area. A magnified study of this specimen May be a future article here. The question is, "What did it hit during re-entry through the atmosphere?".
Australite flanged buttons are the most fascinating and highly prized of all tektites. Flanged buttons with a translucent flange are even more rare. It's amazing to hold one of these little objects in your hand and to try to imagine what special circumstances were involved that allowed this impact event to create tektite glass. What were the dynamics involved to create all these shapes and then spread them over one-tenth the surface area of the Earth. And I almost forgot... Could somebody please find the source crater for this huge event that happened less than 800,000 year ago... It seams to have been misplaced.
In conclusion, we have briefly touched on the topic of the surface texturing of tektites in these last two articles. Much scientific work still needs to be done before we fully understand all the processes involved with these truly unique and puzzling objects of confusion.