Depth of pits
(mm)
What process accounts for the external features of tektites, aerial ablation while flying in the atmosphere or chemical etching after arrival on the Earth's surface? This issue remains debatable for decades.
Surface features of indochinites have generally been considered to be the result of soil acid etching or corrosion. H. H. Nininger and G. I. Huss (1967) published a landmark article in Science magazine, showing internal plasticity of some tektites after completion of their surface sculpturing. These decisive evidences show that tektites sculpturing is done by aerodynamic process rather than chemical etching on Earth., which Dr. J. A. O'Keefe (NASA-Goddard Space Flight Center) advocates. However, there are still different explanations on the phenomena Nininger and Huss pointed out (V. E. Barnes and M. A. Barnes). Their well-known indochinites are unavailable for further study (personal communication with Ms. M. Huss, 1998).
Fortunately, while looking through our collection of indochinites from Maoming, Guangdong, China, we have found some pieces surprisingly similar to those shown on Nininger and Huss's paper. We have collected 50,000 - 60,000 indochinites, with the assistance of elementary school students (P. Liu, 1998). Following are a set of onion-shaped indochinites we obtained in 1997.
Nininger and Huss did not give a detailed description on their bulbous drops that show plastic flattening, which could be one reason that tektite researchers argue about their forming machenism. By looking closely at my specimens, I have found some overwhelming evidences (table 1) supporting the explanation made by Nininger & Huss (1967) and O'Keefe (1967). Those pieces have some common characteristics: (1)bulbous shapes; (2)flow lines visible only on top and convergent to the sharp tip; (3) "raised dots" on top and pits at bottom; and (4) no pits on top, and no "raised dots" or flow lines at bottom.
Table 1. Plastic flattening of some bulbous drops and their characteristics
| Sample # | tpl#1 | tpl#2 | tpl#3 | tpl#4 |
| Photo | |
|
|
|
| Weight (g) | 14 | 46 | 37 | 127 |
| Height (mm) | 30 | 50 | 22 | 30 |
| h/d ratio | 1.20 | 1.67 | 0.63 | 0.46 |
Depth of pits (mm) |
1 - 4 | 1 - 3.5 | 1 - 3 | 1 - 2 |
(h/d ratio stands for height to diameter ratio)
These pieces show a process of gradual flattening plastically, with the ratios of height to diameter ranging from 1.67 to 0.46. Note that the leftmost piece shown above is broken on the tip. Its actual h/d value can be higher.
The flattening affects not only the overall shape, but the flow lines and pits as well. Flow lines (Photo 2) get more convergent on the tip and the pits become flattened and shallower as flattening increased. Photo 3 shows the "bottom" views of the leftmost and rightmost pieces of photo 1.
Photo
1. Flow lines on tpl#2
Table 2. "Bottom" Views
| Sample # | tpl#1 | tpl#2 |
| Photo |  |
 |
It is evident that the flattening process took place while tektites were in flight. No known chemical etching can possibly result in those characteristics. Therefore, we support the point of view that surface sculpturing of tektites is mainly caused by aerodynamic processes rather than chemical etching on the Earth's surface, especially so in the youngest tektites found on Earth like indochinites.
These priceless pieces are accessible for further researches. We hope they will go to a museum or a researcher. If someone is interested in them, please contact us for more information.
References
(1) V. E. Barnes and M. A. Barnes. 1973. Tektites. Dowden, Hutchinson & Ross, In., pa.247-253.
(2) J. A. O'Keefe. 1967. Tektites Sculpturing. Geochemica et Cosmochimica. Vol. 31, pa.1931-1933.
(3) P. Liu. 1998. New Data on Indochinite Tektites in China.Website of Great Wall Consulting & Trading (www.greatwallct.com).
(4) H. H. Nininger and G. I. Huss. 1967. Tektites that were partially plastic after completion of surface sculpturing. Science. Vol. 157, No. 3784, pa. 61-62.