tektites, shapes, strewnfield, different types, variation, morphology,
THE MORPHOLOGICAL VARIATION OF TEKTITES WITHIN A STREWNFIELD
This page has been prompted because it is apparent that some people fresh to tektites have a belief that tektites are all the same. It is clear, however, that certain morphologies and features are restricted to certain geographic areas. Recently in the Philippines I came across 4 kilos of Indochinites for sale, these are distinctly different to Philippinites (and much cheaper)! They were not deliberately passed off as Philippinites, the shop holder, who got them off an uncle, simply didn’t know how to differentiate them (or that there was a difference). For a second time I have now seen low-grade Indochinites in Manila, mixed in with genuine good average Philippinites - it's amazing how man has transported the tektites. Again the seller had simply bought tektites to sell on, unaware of where they came from.
The morphologies and features are directly linked to the distance from the source crater that the tektite has travelled. In some strewnfields it is probable that only proximal forms exist where the impact was closer to the vertical (and perhaps only very limited strewnfields / no tektite strewnfield (dependent on crater size) exists for near-perpendicular impacts). As the obliquity of the impact increases I suspect that Philippinite/Bediasite types are formed. Only with extremely oblique impacts, are australite-types formed. The angle and velocity at which the tektites are ejected are key to their final form. If angle and velocity is too high the tektites will probably be lost to space. With high velocity and low angle then Australite-type tektites will form.
No tektites: Ground zero to 250km from the source crater
Examples: Nordlinger Ries Impact Crater (Moldavites), Bosumtwi Crater (Ivory Coast Tektites).
This area appears to be devoid of tektites. On impact, initially terrestrial rock is vaporised. I then suggest that as the crater formation continues material is shot out at a certain speed and angle, with the temperature in the range for producing tektites. Obviously at a certain angle (defined by the crater excavation) and speed, the tektites cannot land close to the crater. The only material capable of landing close to the crater is material travelling at lower velocities (or higher angle, but this is not likely to happen as material is ‘splashed’ out to the sides). So, material at a lower velocity is likely to be formed later on in crater formation (and thus also at a lower temperature) and secondly the lower velocity will likely result in a bubbly glass. I believe that for tektite glass to form, a high velocity is required, which effectively differentiates gas bubbles from the tektite glass (think of a centrifuge), thus forming a very pure, good quality glass in an extremely short time. Interestingly this distance from crater to first tektites, at a set (estimated) angle, might tell you the velocity the tektite travelled and thus the velocity required to remove the bubbles from the glass.
This NASA image shows what happens in an impact. You might not expect the initial molten material shot out of the forming crater to land anywhere nearby. I suspect that only later formed, lower velocity, probably less melted projectiles would land close by. Please click here to visit the NASA Deep Impact website.
Proximal splatforms and splashforms: roughly 250km to 1500km from the source crater.
Examples: Ivory Coast Tektites, Indochinites, Georgiaites, Moldavites (heavily etched).
Types found: Patty shapes (discs, often concavo-convex or bi-concave); dumbbells; spheres; teardrops; irregular forms; shells; Moung Nong (very large layered forms); Onions and Hershey’s Kisses (teardrops landing semi-molten).
Features seen: Very common bald spots and associated wedge shapes; common starburst and radial rays; very rare skin splits; common pitting on surface; common smooth forms; common bending/relaxing resulting in mis-shapen/flatter forms.
Intermediate plastic splashforms: roughly 1500km to 3000km from source crater.
Examples: Philippinites, Billitonites, Bediaisites.
Types found: Large un-grooved/smooth spheres/nuclei (always un-grooved/smooth over c.350-400g); breadcrusts (in 130-350g range); biscuit-disc form (occasionally oval) (biconvex with one grooved side) (under 100g, typically 30-60g); uncommon dumbbells (grooved one side); uncommon teardrops (grooved one side); common spheres, commonly more grooved on one side; shells (grooved on convex side); rare small grooved ovoids.
Features seen: U-grooves extremely common (unusual on large specimens over 350g, sometimes not on smaller specimens, but skin is relatively smooth in these cases); very rare bald spots; very rare radial grooves (to possibly starburst rays); occasional impact fractures; common navels (very common on biscuit forms and some spheres under 100g, practically absent on other shapes).
Solid, aerodynamically shaped splashforms: roughly 3000km to 7000km
Examples: Australites, some tektites from Java, one example in Indian Ocean.
Types found: Flanged buttons (always under 4g); cores; spheres; shells and loose flanges. Flanges and cores form from discs/spheres, ovals, dumbbells and teardrops.
Features: On cores grooves may be found together with some navel evidence. Flanges typify this type of tektite, but perfect specimens are rare. Typically tektites in this part of the strewn field are small, under 15g, but can be larger. No impact features noted due to probable solid landing.
Micro-tektites: over roughly 7000 km
Micro-tektites are found throughout the strewnfield, but only micro-tektites (no Macro-tektites) are found in the most distal areas. May be wind aided.