Tektite, anda, australite, philippinite, rizalite, bikolite, bicolite, indochinite, strewnfield, formation, sculpture, australasian, sale, bristol, impact, asteroid, meteor, meteorite, orientation, navals, grooves, bald, stretch, tektites, aubrey, whymark, splatform, splashform, ablated, plastic

PHILIPPINITE SCULPTURE: OBSERVATIONS

Philippinites are grooved. These grooves form straight or curving lines and have been termed ‘gutters’, ‘U-grooves’ and ‘worm tracks’. I will refer to them as U-grooves. Where these U-grooves form a circle they are referred to as ‘Navels’. ‘Navels’ can be in isolation or connected to a U-groove: they are clearly closely associated and will be considered together.

Some observations of Philippinite surface sculpture:

 

ABOVE:   Side view of a biscuit. The posterior is the smooth upper surface and the anterior is the grooved lower surface.

Observation: U-grooves and navels do not have a random distribution. In most cases they occur on one side of the body only. The other side is usually smoother or smooth.

 

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ABOVE:   The grooved side of a Philippinite biscuit.

Observation: Navels occur on the same side as U-grooves and their typical or idealised distribution is roughly mid-way from the edge to the centre of the sphere/disc. Non-random distribution excludes random events leading to their formation, such as impact by other tektite bodies.

 

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ABOVE:   A biscuit and a breadcrust Philippinite

Observation: U-grooves occur from the edge of one side of the sphere/disc and trend towards the centre, but usually die out before reaching the centre. In larger bodies they form polygonal (pentagonal or hexagonal) patterns with the lines on the edges joining up with a central polygon. On even larger breadcrust specimens they are polygonal all over, but polygons are smaller on the edges and bigger on the front and back.

Polygonal shapes are commonly associated with cooling (e.g. basaltic columnar lava) or contraction due to de-watering (e.g. desiccation cracks).

ABOVE:   An example of polygonal jointing in basalt at the Giants Causeway, Ireland.

 

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ABOVE:   Biscuit Philippinites showing a polygonal pattern on the grooved surface. The specimen in side profile is the same specimen as that seen in the bottom left of the four specimens with a face-on view.

Observation: Occasionally on the anterior side of biscuit forms a clear polygon is formed, surrounded by U-grooves/gutters. The posterior side is smooth.

 

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ABOVE:   U-grooves are fresh in appearance against an older pock-marked surface

Observation: U-grooves always appear fresh, relative to the main outer surface of the tektite. This might suggest that U-grooves formed after the main outer surface, not at the same time.

 

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ABOVE:   A deeper groove cuts a shallower earlier formed groove.

Observation: On large tektites (e.g. breadcrusts) some deep U-grooves cut older shallower U-grooves. The deeper ‘cutting’ U-groove has to have formed after the shallower ‘cut’ U-groove. There must have been more than one phase of crack/groove formation – it was not instantaneous.

 

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ABOVE:   Shallower 'cut' grooves appear to be more pock-marked than deeper 'cutting' grooves.

Observation: The shallower ‘cut’ U-groove subtly appears more pock-marked than the deeper groove. More study and a larger study-set would be required to quantify this and assess whether it is genuine.

 

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ABOVE:   'Flow' lines on the outer surface continue across the grooves.

Observation: ‘Flow lines’ cross U-grooves, usually in a perpendicular fashion. These ‘flow lines’ are developed within the glass of the tektite, not a surface ornament. The ‘flow lines’ on the U-grooves join up with ‘flow lines’ on the outer surface of the tektite.

The flow lines do not appear to be 'stretch marks'. If they were, they should have no relationship with the flow lines on the outer surface. Additionally, this indicates the U-grooves formed after solidification of the outer surface and have been gouged/ablated out or are due to chemical etching.

 

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ABOVE:   A spherical breadcrust with material evidently missing in the U-grooves. On the same specimen a 'failed' U-groove is seen to half penetrate a polygonal shell.

Observation: I have attempted to join up adjacent segments on breadcrusts by surface features. I do not believe they join up. This implies they are not simple cracks, but material is missing between them. In places U-grooves terminate abruptly within a polygon, proving that material is missing between them and these are not simply wide cracks. Further proof comes from spherical bodies – if the cracks were joined together they would not be spherical. If the cracks are filled in the body is spherical. If these were originally cracks they were paper thin and have been widened (by removal of material) via another mechanism such as ablation or etching.

 

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Observation: The U-grooves are sharp. If due to ablation, one might expect them to be more rounded.

 

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ABOVE:   A nucleus Philippinite with a smooth appearance, formed following loss of it's grooved shell. 

Observation: The biggest of all tektites in the Philippines (over about 400g) are never grooved. Smaller specimens may also form smooth nuclei. It has been suggested that the biggest specimens are the most thermodynamically unstable, thus resulting in the outer grooved shell splitting away from the cooling ‘nucleus’. Grooves do not reform on the nucleus.

 

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ABOVE:   A shell fragment from a large Philippinite against a smaller biscuit Philippinite

Observation: In general, U-grooves appear to be wider in larger bodies, although to pick up the average change you require significantly different sized bodies.

 

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ABOVE:   Deep U-grooves on a larger breadcrust against shallower U-grooves on a biscuit-form.

Observation: As a rule of thumb, the bigger the specimen the deeper the groove. If the process of groove formation is purely ablative this does not make sense. If ablation or chemical etching enlarged a pre-formed crack this makes more  sense. Pre-formed cracks would be expected to be deeper on larger specimens.

 

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ABOVE:  A shell fragment that has cooled more on the interior where a U-groove exists on the exterior. When the shell breaks away a new U-groove would be left on the nucleus.

Observation: Usually when the shell breaks away from the nucleus it has a smooth concave surface leaving a smooth nucleus. In some cases, however, where the U-groove is on the outer surface a ridge is visible on the opposite smooth concave surface – this would undoubtedly leave a new groove on the exposed nucleus. This is suggestive that the nucleus was still plastic and that if the cooling penetrated ‘x’ distance into the specimen, then the grooving/cracking occurred whilst the nucleus was semi-molten. Because of the crack, material further into the specimen was cooled.

 

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ABOVE:   U-grooves forming on the underside of shell fragments.

Observation: Poorly developed U-grooves (not forming a distinct pattern or penetrating deeply) may occasionally form on the smooth concave side of the shell that has broken away from the nucleus. These appear unrelated to those on the outer convex surface of the shell.

 

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ABOVE:   An example of a U-groove joining a navel.

Observation: Navels, occur on the grooved anterior side, most typically on biscuits. They often join on one side (not the middle) to a U-groove. The U-groove usually cuts the navel on the edge closest to rim of the biscuit, then joins the navel, which swirls around to the cut-off point. Usually, under magnification, the U-groove terminates at and overlies the navel, rather than running perfectly smoothly into it. On the same specimen these can be both clockwise and anti-clockwise. Navels are discussed in greater detail on the 'Philippinite Grooves and Navels' page.

 

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ABOVE:   A teardrop Philippinite showing spiralling U-grooves.

Observation: On two Philippinite teardrops I have seen U-grooves on half of the long axis, with the U-grooves oriented in a similar manner and each curving, or spiralling, away from a central point (which they stop (or start) prior to meeting at).

 

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ABOVE:   Anda (subtype II) texture occurring in a groove on a nucleus-like body. 

Observation: Anda-type sculpturing can occur very rarely on U-grooves. Anda sculpture is now clearly established as being due to chemical etching. The fact it overwrites the U-groove sculpture shows that the U-grooves came first - either formed in flight or due to a different etching process prior to the formation of Anda sculpture.

 

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ABOVE:   Grooves of various sizes on a biscuit Philippinite.

Observation: There are longer and ‘failed’ shorter U-grooves coming from or going towards the rims of biscuits. If shorter U-grooves exist towards the rim it might suggest that the grooves started at the rim then grew towards the centre of the biscuit, but this is inconclusive.

 

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ABOVE:   Philippinite dumbbells, larger specimens typically broken in half. One side has deeper grooving than the other. Sometimes the deeper grooved side shows evidence of spalling, creating a dumbell core.

Observation: In dumbbells the deepest grooving occurs on the anterior. The cracks or grooves create a line of weakness, often resulting in the tektite snapping in two close to the centre of the dumbbell.

 

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ABOVE:   The smooth side of a biscuit Philippinite.

Observation: Ablation in wind tunnels typically produces a smooth surface. The smooth surface of Philippinites is not, however, produced by ablation. The smooth side in fact represents the untouched primary posterior surface.

 

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ABOVE:   The Apollo-9 re-entry vehicle

Observation: The smooth surfaces of biscuits are remarkably uniform and look like the blunt re-entry Apollo craft. Again, this is misleading as the smooth side of Philippinites is actually the posterior. The key factor at play in tektites is not ablation, but the way that glass reacts to rapidly changing temperature. This results in cracking and spalling.

 

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ABOVE:   A navel-like feature on an Indochinite from Vietnam.

Observation: Navels rarely appear on one side of some Indochinites, but no U-grooving is observed.

 

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ABOVE:   A small oriented meteorite. Note the smoothed surface. 

Observation: In meteorites the overall effect of atmospheric entry is to smooth the shape. Meteorites, however, are not made of glass and react very differently to thermal stresses during re-entry. In Philippinites the smoooth surface is in fact the posterior.

 

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ABOVE:   A large oval Indochinite. Even large Indochinites do not exhibit U-grooves.

Observation: Polygonal grooves do not occur in Indochinites. This indicates that groove formation is not a simple cooling process, otherwise all tektites would have them. Cooling and contraction joints could be a factor, but the principal process appears to be related to thermal stresses during re-entry.

 

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ABOVE:   An example of a broken Australite button.

Observation: Polygonal grooving does not occur in Australites

Observation: Flanges in australites can re-form after loss of the stress shell. This is suggestive that the tektite may lose it's stress shell early on in flight and then continue to ablate. It is clearly not a process restricted to the very last stages of flight where the tektite might be cooled by the air flow once inherited cosmic velocity is lost.

 

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ABOVE:   An example of an oval Australite core. The first photo shows the anterior surface and the second a side view.

Observation: Grooving is seen on the anterior of Australite cores along with navel-like features. This grooving appears to be directly related to the spalling process. U-grooves are also occasionally seen on the posterior of Australites. The shape of the grooves appears similar to those in Philippinites. The anterior surface of Australites is indisputably established. The spalled part of the core is the anterior surface.

 

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ABOVE:   On this biscuit Philippinite the U-grooves are cut sharply.

Observation: On the edges grooving does not carry on around – there is a sharp division between the smooth and grooved side.

 

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ABOVE:   Navels only occur on oriented specimens such as biscuit Philippinites

Observation: Navels are almost entirely restricted to what appear to be oriented specimens and typify cores/biscuits.

 

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ABOVE:   Bald spots on oriented Philippinite breadcrust indicators and smaller biscuit forms.

Observation: Bald spots have been noted as occurring on the smooth side of some medium and large Philippinites. This feature was first noted by Henry Otley Beyer. The specimens illustrated not only show flattened bald spots, but also cracks developed at the time of impact. Note that in both cases the bald spot is on the smooth side, off-centre. This is studied in more depth on the 'Impact Features' page. It is suggestive that some Philippinites, including medium-sized specimens, were still plastic when they landed. If this is the case, they were therefore also plastic during flight.

 

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ABOVE:   Possible starburst/radial ray features observed on Philippinites

Observation: Possible starburst/radial ray features have been observed on Philippinites. This is studied in more depth on the 'Impact Features' page.

 

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Awaiting Image - Do you have a Breadcrust Bomb Image I can use?

Observation: Breadcrust volcanic bombs superficially resemble breadcrust Philippinites. An example can be found at http://volcano-pictures.info/glossary/bomb.html. An image google search provides many more examples.

Interpretation: Breadcrust volcanic bombs are formed due to expansion of the brittle solidified outer shell. Expansion occurs as gas bubbles form. Gas bubbles come out of solution due to the reduced pressure on eruption. Given that tektite glass is largely bubble free this idea would seem unlikely, but is certainly worthy of further investigation. An interesting point is that  a polygonal structure is formed by expansion on the breadcrust volcanic bomb. The cracking on the volcanic bomb must occur along pre-existing lines of weakness. Another method of attacking the lines of weakness may be at play in breadcrust tektites. Additionally, it is noteworthy that this breadcrust sculpture does not occur in the proximal Indochinite tektites.

 

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Observation: Using candle wax which is solid on the exterior but liquid on the interior, when cooled the wax contracts creating U-shaped holes or grooves. Could the exterior of the tektite be solid with red hot cracks that are still molten. When cooled this material contracts and sinks in towards the nucleus? The author considers this to be unlikely. If this is the mechanism of formation, U-grooves might be expected in Indochinites.

 

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ABOVE LEFT:  A teardrop which is unusally (for the Philippines) asymmetrical. The natural orientation would be the grooved side down.  ABOVE RIGHT:  A large bulbous/conical teardrop. The natural orientation would be blunt side (grooved side) down.

Observation: These very rare, excellently formed, Philippinite tear drops should have a known fall orientation (blunt end forward). These are suggestive that the grooved side is in the anterior.

 

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ABOVE: A core, front and back. Good flow swirls on one side (right) means this is the untouched posterior side. Spalling on the other side (left) also incorporates navels. This is the anterior surface.

Observation: I have recently acquired further examples of Philippinite cores. In these examples (above) the navels clearly occur on the spalled surface. Again these specimens suggest that the grooves and navels occur on the anterior.

 

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ABOVE: Very thin navals and U-grooves on an apparently chipped surface

Observation: In some batches of Philippinites that I have seen (and I am uncertain of the original locality, other than that they were bought together), the grooves and navels are very thin and crack-like. Some of these specimens come from Paracale, Camarines Norte.

 

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ABOVE:  An extremely rare navel, with shell attached. This indicator form is certainly a big clue as to how navels formed! It came from Paracale, Camarines Norte, Bikol.

Observation: Firstly, on this specimen flow lines flow through the navel and appear unrelated. Secondly, a very rare (maybe 1 tektite in 50kg) piece of shell is attached to a navel. It is uncertain whether the loss of the shell of this specimen is original from flight or due to later chipping of the specimen.

Interpretation: This specimen (and one other similar specimen I have) indicate that navels are related to shell loss and represent the last attached area. It is probable that etching has enhanced this feature. This strongly indicates that the grooved side of Philippinites is the anterior.

 

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