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

ANDA SCULPTURE

(AND V-GROOVES)

 

 

ABOVE:   ?Pre-Anda Sculpture. This kind of skin seems to be closely associated with Anda's and is commonly found on nuclei. The top left specimen is questionably Anda, whilst the bottom right specimen clearly exhibits Anda sculpture. All these specimens are from the Philippines, probably the Bikol region.

 

ABOVE:   Anda subtype I. Hemispherical pits with ‘rodent gnawing’ marks radiating from the centre. This example is from Vietnam, but the same texture can occur in other Indochinites and in Philippinites.

 

ABOVE:   Anda subtype I to II. Hemispherical pits to grooves with ‘rodent gnawing’ marks radiating from the centre. These specimens are from Thailand, but the similar texture can occur in other Indochinites and in Philippinites.

ABOVE:   Anda subtype II (Pangasinan subtype in Beyer, 1962). Fine ‘rodent gnawing’ grooves, but occurring over the whole of an often concave surface/side. A trace of Anda subtype I can be seen middle left of the specimen. This example is from Pangasinan, Philippines.

 

ABOVE:   Anda subtype II to III (plus almost subtype I) clearly showing well developed Anda subtype III, intermingled with Anda subtype II (almost grading to Anda subtype I). This example is from Pangasinan, Philippines.

ABOVE:   Anda subtype III (Pangasinan subtype in Beyer, 1962). Coarse V-shaped grooves develop, again having a clear central focal point.

 

ABOVE:   A Besednice Moldavite. Compare this sculpture with the Anda sculpture above.

Anda tektites are highly prized in the tektite world and understandably so. The Anda subtype I are beautiful and enigmatic objects. They have an organic, coral-like appearance. When I first saw a specimen I was convinced it must form due to a secondary process on the ground, I then changed my mind, thinking it occurred late on in flight with the central point being a stagnation point. Now I am convinced that Anda sculpture arises through chemical etching in the ground. The pattern clearly grades from subtype I to III and is probably found across the strewnfield. Anda grooves come in various sizes, but are typically V-shaped and radiating from a central point.

The term Anda subtype was originally coined by Henry Otley Beyer in 1954. The name Anda was given as these tektites were found in the Anda area of Pangasinan, Luzon, Philippines. It was initially considered that these forms were restricted to this area, however, they have been found at other localities in the Philippines including the Bikol region and also in the Indochinese Peninsula (China, Vietnam and Thailand - certainly subtype I and II anyway). The Anda texture links into the V-grooves of Australites, described in McNamara, K, and Bevan, A. 1991. Tektites. On page 18, V-grooves are described: 'these are most common on remnants of the primary surface, constituting the rear surface of flight. When abundant they may form a pattern radiating from the centre of the surface'. A paper by Cleverly, 1986 entitled 'Australites from Hampton Hill Station, Western Australia' has excellent plates showing Australites with V-grooves/'Anda' sculpture primarily on the posterior surface

In Beyer’s 1954 paper he actually uses the term Anda subtype (applied to my subtype I) and Pangasinan subtype (applied to my subtype II and III). I use the term Anda to define the sculpture type (which was first described from Anda) and not to imply any geographical inference. The term Anda is now commonly applied to my Anda subtype I and II and to a lesser extent my subtype III, which are also referred to as Moldavite or Besednice-like (Besednice Moldavites have a similar sculpture, but are plastically deformed). The term Pangasinan subtype has fallen out of favour and I have never heard it used. The three subtypes are clearly related, with a single specimen seeming to almost show all three textures. Subtypes I and II seem extremely closely related and probably formed by the same mechanism, but in slightly different circumstances. There is likely a progression or evolution from subtype II towards subtype III.

Anda tektites are expensive, this reflects their rarity and beauty. Why has the texture only developed on a few specimens as oppose to being a common feature. What is special about these specimens, how does their history differ from other specimens? I am currently thinking that to develop Anda sculpture the tektite may need to be exposed to fresh water, perhaps of a particular pH. It would appear that Anda tektites are associated with porous and permeable sands and gravels. Further study is needed on this front as most tektites are removed/not in situ and therefore are not found in context.

Here are a few observations on Anda Sculpture:

1) It occurs in Vietnam, Thailand, China, Philippines. Radial V-grooving in Australites and Besednice Moldavite texture is effectively the same as Anda Sculpture. The latter is widely accepted as being due to chemical etching. Some Bediasites from the North American strewnfield also exhibit Moldavite-like V-grooving.

3) It appears to overwrite all other sculpture including Indochinite starburst rays (assumed to be produced on impact with the ground) and Philippinite U-grooves (formed by loss of the stress shell). On a single specimen, however, it did not appear to overwrite a plastic split. It is distinctly less prominent on wedge-shaped bald areas and shell-loss areas.

4) It forms a very non-random radiating pattern. It usually radiates from a concave surface. It sometimes radiates from a central pit. When developed it usually occurs on all surfaces of a specimen, although it is better developed on one side (the posterior). It commonly occurs on the edges of broken 'bubbles'. In teardrops the pattern appears to always be the same - this applies to Indochinites and to Moldavites. If due to etching it is not random but follows pre-defined lines of weakness, which I suspect are due to cooling.

5) In some cases Anda sculpture follows, or broadly follows, flow lines, but in other cases internal flow lines are very clearly cut.

6) It has been stated (although not confirmed first hand) that in Anda (Pangasinan, Luzon, Philippines) 60-70% of tektites exhibit Anda Sculpture. The soil was described as yellow sands by a non-geologist. Are highly porous and permeable sands/gravels, perhaps containing fresh water, a key ingredient to the formation of the sculpture?

7) There are numerous stages of Anda sculpture formation. Initially a rougher surface, then Subtype I (fine, discreet), closely related and grading to subtype II (fine) then grading to subype III (coarse). A single specimen may exhibit all of these subtypes.

8) I have not, to date, seen Anda sculpture on oriented biscuit-form Philippinites. Anda-like sculpture in Australites commonly occurs on the primary surface - the posterior of flanged buttons/cores. I am guessing it follows lines of weakness, only present on the primary posterior surface, destroyed by re-melting/ shell loss on the anterior surface. It would be very interesting to see how Anda sculpture develops on a true biscuit-philippinite - it would be expected to be best developed on the posterior. Interestingly Anda sculpture neatly solves a problem in Indochinites - the posterior will have the best developed Anda sculpture.

9) In Philippinites, Anda sculpture appears to be most commonly associated with irregularly shaped (?fragmented) specimens and large (over 400g) 'smooth' nuclei. I have not seen it developed on breadcrusts, although it may occur. I am wondering if atmospheric passage and remelting/ shell loss of the exterior surface somehow makes specimens impenetrable to Anda etching (like the anterior of australite buttons). The sculpture may only attack, or preferentially attack, surfaces not subject to re-heating/spalling.

10) On areas that I have interpreted as cracks on Philippinites, related to impact, sometimes a radiating 'crystal'-like structure is seen. On a medium sized broken Philippinite, again a radiating pattern is seen internally. I think this radial pattern is related to cooling of the tektite from outside-in - this explains the very consistent pattern on shapes such as teardrops. Bubbles in specimens would also create strained areas around them. Possibly a radiating patten might also be formed by impact (at time of formation or afterwards). Anda sculpture appears to be following an internal radiating pattern.

11) Anda scupture is best described as delicate and Besednice Moldavite texture is very delicate. It is impossible to imagine these specimens to land with such delicate sculpture - it simply would not survive. Anda's are very quickly damaged when freed from the rock in which they have rested.

12) Anda sculpture has the appearance of cutting into specimens, i.e. removal of material. This was highlighted in the fresh specimens I acquired from near the town of Anda via Desmond Leong of www.tektiteinc.com. This is much less obvious in even slightly weathered/ water worn specimens.

13) Anda sculpture does not appear to occur on bald spots of Indochinites. Possibly the impact / shell loss that created the bald spot also obliterates any existing lines of weakness that would have been prone to chemical attack. The bald spots represent the anterior surface.

14) Anda sculpture in Philippinites, in it's initial stages (as it forms subtype I), often has a sigmoidal shape. This is similar to a tension gash. I have also observed similar sigmoidal cracks in glass - please see my Analogues page - Cracked Glass. Cleverly, 1986, also observed these sigmoidal cracks in Australites.

 

ABOVE:   Anda sculpture (subtype I (to II)) apparently occurring on a starburst ray feature, which is believed to have formed when the tektite impacted the ground. This tektite is from Thailand.

 

What causes the radial pattern? This is an interesting area of research. I suspect it is linked to cooling of the tektite, creating an internal radiating pattern and strain in the process. Sometimes sigmoidal cracks form and these seem to be the precursor to Anda subtype I sculpture. Around a bubble a strain pattern also develops. Maybe shock (on impact) might also create a radial pattern for the sculpture to follow. Some tektites broken by humans show a radiating pattern (not to be confused with a conchoidal fracture). Also radial patterns are commonly seen on what I interpret as impact fractures. See below.

ABOVE:   Impact fractures which either caused or exposed a radiating internal pattern to the tektite.

ABOVE: A Philippinite that shattered during cleaning in water (it was not struck - at least not at time of cleaning). It appears to radiate from a ?bubble point of weakness.

ABOVE:   A radiating structure formed in an ice cube as it cooled/solidified. For more images see the Ice Cubes Analogues page.

 

ABOVE:   Sigmoidal cracks in a curved glass window of a cable car and sigmoidal V-groove on a Philippinite exhibiting Anda-type sculpture. For more images see the Cracked Glass Analogues page.

 

SUMMARY: The current evidence suggests that Anda sculpture is developed due to chemical etching in the ground. This will be strongly linked to the porosity and permeability of the rock and pH of the groundwater. Anda sculpture is not random, but follows pre-defined lines of weakness, or strain, probably related to rapid cooling from the outside-in. This cooling created a radiating pattern. Re-melting and shell loss through atmospheric passage may guard against chemical etching by destroying the lines of weakness. I believe that Anda sculpture is effectively the same as radiating V-grooves in Australites and V-grooves so commonly developed in Moldavites. V-grooves have also been noted in North American Bediasites.

In order to test this further it would be interesting to drop a few tektites into ammonium flouride or hydroflouric acid. Also to deliberately chip or strike/fracture areas on the tektite and then drop into hydroflouric acid. I think this is important not only to test formation but also to test if fake Anda tektites could be made and identify the difference. Please note that Hydroflouric acid is extremely dangerous (if 10% of your skin is exposed to the acid you are dead), so it should only be used in a laboratory, fully covered up (and double gloved) with the strictest safety measures enforced.

  

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