| ‘Billitonite’ is a western name for tektites from Belitung Island in Indonesia (pronounced Bill-it-ung). The island was formerly known as Billiton Island and was part of the Dutch East Indies. In fact this is where the mining giant BHP Billiton derives part of its name. In 1860, the company, then just Billiton, acquired a concession to the tin-rich Billiton (now Belitung) island. This tin mining still goes on today and this is why tektites are found on this island. The tektites are locally referred to as Satam Stone, or sometimes Batu Satam. The word Satam comes from the language of the descendents of Chinese people who came to Belitung for work in the tin mines. SA means sand and TAM means gall: so Satam means bile sand (1). On visiting the island, locals are keen to tell you that Satam Stone is only found in Belitung. This is what people believe, and you are not being lied to; however, this is only a partial truth. In Indonesia, tektites from the same impact can be found in several places in Kalimantan (Borneo), Natuna Islands, Gourd Island, Java Island aswell as Belitung Island (2). Barnes, 1963, reports Indonesian tektites from Kalimantan (Borneo) at Riam, Pleihari, Martapura and Laut; from Java Island at Sangiran and Japara and on the island of Flores at Mataloko. Outside of Indonesia tektites from the same impact are found in southernmost China Guangxi, Guangdong and Hainan provinces, Laos, Vietnam, Thailand, Cambodia, Myanmar, Philippines, Malaysia, Brunei, Australia and with microscopic tektites reaching as far as Antarctica. The tektites in these different countries and localities have different forms and surface sculptures. This is principally a product of distance from the impact source –ground zero. The subsequent weathering, abrasion and chemical etching of the tektite, largely dependent on the rock and water chemistry in which the tektite is encased, will create further localised differences in tektite sculpture. The Southeast Asian tektites were derived from an as yet undiscovered impact crater in Indochina, most likely located in the Bay of Tonkin. The Southeast Asian tektites can effectively be divided into 3 broad groups. Firstly the Indochinites which include tektites from Southern China, Vietnam, Laos, Cambodia and Thailand. These forms re-entered the atmosphere in a molten state, most molten in North Vietnam, Southern China and Northeast Thailand. Due to their molten re-entry they deformed into donut and onion shapes and suffered only limited thermal breakage of the anterior during re-entry. The second subset, at intermediate distances from ground zero, includes Billitonites or Satam Stone, and Philippinites and Malaysianites. Basically tektites from Northern Indonesia, Malaysia and the Philippine Islands. These tektites re-entered the atmosphere as solid glass spheres. Frictional heating during atmospheric re-entry resulted in considerable spalling of the tektite body, leaving cores or ‘biscuits’. The third subset, the most distal of the tektites, are the Australites. Similar forms also extend to the southernmost Indonesian areas (Java, Flores). These tektites, probably travelling at the greatest velocities and shallowest angles of re-entry and also entering as solid bodies, formed cores and the classic ablated button shape tektite. Further afield, in Antarctica, only microtektites are found. Larger tektites would have been totally ablated away at this distance from the source crater. So, Billitonites are tektites which formed at intermediate distances from the source crater and share common traits with tektites from Malaysia and the Philippines. In fact, if you muddle a lot of these tektites up you would struggle to tell the difference between a Billitonite and a Philippinite. Interestingly, whilst some are identical, a percentage of Billitonites are subtly different to the average Philippinites in that they have far more U-grooves than the average Philippinite. Why do billitonites have more U-grooves than Philippinites? It may be that Billitonites formed marginally further from the source than Philippinites and are thus more cracked by frictional heating during re-entry. Billitonites were probably flung around 2,400 km from the source crater, Philippinites from Paracale some 1,700 km from the source crater and Philippintes from Davao some 2,400 km from the source crater. It is interesting to compare Desmond Leong’s ‘Shrek’ specimen from Davao with the Billitonites. Note that on this page the anterior with the projections is at the top. It would also be great to find a source for deeply etched specimens in Davao/Mindanao in the Philippines and compare these with Billitonites. The Philippinites currently coming from the Davao region are generally not deeply etched (less terrestrial alteration), which is equally pleasing. An alternative suggestion as to why Billitonites have more U-grooves than Philippinites is that Billitonites may simply be less transported by terrestrial processes than the typical Philippinite, most of which come from Paracale, Bikol. If you ignore the chemically etched U-grooves then Billitonites, in general, appear less water worn. Phillipinites from Paracale, if water worn prior to etching, would have less cracks to attack and form U-grooves. In these Philippinites the abrasion may remove the top layer and so all small cracks are lost and only deeper cracks remain for chemical attack. More research needed on this front, but I think this scenario is less probable than it being a simple function of distance from the impact site. I would expect to see rare Philippinites from Bikol with many U-grooves like Billitonites if the sculpture was purely down to degree of water transportation prior to etching. In Belitung the tektites are also, on average, smaller than those from Paracale, Philippines. I am told that no large breadcrust types are found. This is interesting. Belitung is some 700 km or so further from the impact site than Paracale, so on average one would expect smaller tektites and less breadcrusts. It appears, however, that breadcrust tektites formed from the same size spheres as ‘Biscuit’-forms. Perhaps the breadcrust forms were just perfect spheres and so initially (until a breakage/spalling occurred) had no fixed, stable flight orientation during early stages of re-entry. This being the case, given that we find 96g ‘biscuits’ in Belitung, pretty much the maximum size they can be, then very very rarely I would expect a breadcrust form in Belitung. These may not be found since the rarity of tektites in Belitung means a smaller sample set to work with. After this trip I am very keen to obtain tektites in Mindanao, Philippines. This is where my wife is originally from and we will have many guests from Mindanao at our church wedding in February (we had a civil wedding earlier as I’m a foreigner). I will have to ask everyone to look for tektites! Barnes V. E. 1963b. Tektite strewn fields. In: O'Keefe J. A (ed.) Tektites. Univiversity of Chicago Press, Chicago. 25-50. |
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