An Article In Meteorite-Times Magazine
by Paul Harris

Surface Texturing On Tektites - Part-1

This month we look at factors affecting the surface texturing of tektites.  There is still confusion concerning how surface features on tektites form.  There is no doubt that certain soil conditions have corrosive actions affecting the external appearance of tektites.  We can also confidently say that surface texturing on many tektites occurred during the formation process and that little surface weathering has taken place since the impact event occurred.  Still others, for example the grooved Philippinites exhibit grooves which many feel are a result of chemical etching but differ greatly from the grooves formed by corrosive soil on the Anda type Philippinites.  We will also explore our theory on how corrosive soil affects the surface texture on tektites over time.

First, lets look at the two half disk specimens below.  Apart from the grooves on the left specimen we see little difference in the external surface of these two Indochinite specimens.

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When the two specimens are turned on their sides, we can see the fresh shiny break and large bubble cavity on the left specimen.  The specimen on the right exhibits the same minor surface weathering as seen in the above image. 

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While the above images show how minor weathering can occur, the images below show how the surface features developed during the formation process and have changed little over the course of nearly 800,000 years.  Below are casts of the famous Nininger and Huss Indochinite specimens showing a break while the specimens were still plastic.  Note that the surface texturing is lacking on the area of the plastic breaks.

If the texture on these two specimens was caused by chemical etching, then the area where the plastic break occurred should also have the same surface texturing.  But they do not.  Therefore the surface features exhibited on these two specimens occurred during their formation and not due to chemical etching actions other than very minor weathering..

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Three of the four strewn fields have specimens that are highly sculptured.  Many of the Philippinites of the Australasian Strewn Field,  the Czechoslovakian Strewn Field, and some of the Bediasites of the North American Strewn Field.  I have not seen enough Ivory Coast specimens to know if there are highly sculptured specimens contained in this strewn field.  Of the Philippinites, we will only be looking at the Anda type and we will leave the grooved Phillipinite type for Part-2 of this article in next month's issue.  Over the years we've marveled at the sharply grooved Anda, the beautifully sculptured Moldavite and the prized grooved Bediasites.  While all three exhibit their own distinctive sculptured shapes, it occurred to me that the actions of chemical etching on the tektite glass could have a similar action on the specimens of the different strewn fields.  Two factors to consider are the degree of the corrosive action of the soil and the length of time involved.  While I do not have the soil data, we do have the tektite strewn field ages.

View the 3 specimens below and visualize how the corrosive soil would attack the tektite glass.  Now look at the texturing on each specimen below and rank them in terms of time exposed.  I choose specimens which did not exhibit signs of mechanical weathering, example being river worn.

 

It appears that the Anda has been exposed for the least amount of time.  The Bediasite shows the longest exposure, and the Moldavite is somewhere in between.  This correlates with the ages of the Strewn Fields to which these specimens belong as shown in the table below.. 

Strewn Field Source Crater Age Specimen Close Up
Australasian ? .78 million years Anda
Czechoslovakian Nordlinger Ries 15 million years Moldavite  
North American Chesapeake Bay 35.5 million years Bediasite

The Australasian, Czechoslovakian, and North American Strewn Fields all contain specimens that vary from little if any weathering to specimens which show severe corrosive actions on the surface texture.

Next month we will tackle Part-2 of this article and look at the deeply grooved Philippinites and Flanged Australites.  I will also attempt to produce a Tektite Surface Feature Flow Chart.  These are just the Author's personal thoughts by visual inspection.  We welcome your views, thoughts and comments (pro or con) on the ideas presented in this article and in next months Part-2.