by Erland Damgaard Jensen ©

Fig. 1. Two sides of intermediate tektite showing plastic interior.Shells with breaks and plastic interior.

Fig. 2. Shells, elongated forms, round forms and lids (Top shells). Streach marks on stick and teardrop. Streached airbobbles

Tektites are natural glass objects with weights from micrograms to few kilos. They are found in 7 main strewnfields, Australasian, Czechoslovakian, North American, Ivory Coast, Libyan, Irgiz and Aouelloul. The Australasian field is by far the largest, covering parts of Australia, Malaysia, Indonesia, Thailand, Laos, Cambodia, China and Vietnam. They are divided into four types, microtektites, splashforms, Muong Nong and ablated. The creation and formation of tektites found on earth has been discussed for more than a century. Two main theories of lunar and Earth origin have been dominant, both claiming a large meteor impact be the basic mechanism of formation. This study of 203 Vietnamese splashform tektites proposes a new theory for their formation. The splashform tektites are classified into 3 groups based on their creation; primary, shell and nuclei tektites and into a number of secondary groups based on their forms. The creation and form variations can only be explained by a meteoroid impact on Earth. The primary groups of elongated forms have been well described before as a result of rotation around 1, 2 or 3 axes. Spinforms would be a good name for the group. The two new creation groups, shells and nuclei, are explained by intermediate forms of the primary group that cracks and thereby creates the two final forms of tektites. This cracking is possible because of a liquid or plastic interior (nucleus) in the intermediate form. Evidence of this is found in the structure and form of the tektites. A travel through space from the Moon to the Earth could not leave a liquid interior in these small objects and thereby eliminates the lunar theory of origin.

The two basic theories for creation and formation of tektites found on the Earth both claim a large meteoroid impact be the basic mechanism. Only meteoroids above a certain size have enough kinetic energy to create tektites, dependent on its size, velocity at impact and the impact angle. Meteoroids with impact angles larger than 10 degrees will generally create circular craters varying from simple craters to crates with a central peak and to craters with one or more rings structures, depending on the kinetic energy at impact. Debris from these craters will form a circular ejecta with distinctive radial lines. Impact angles below 10 degrees will generally produce elongated oval shaped craters with a butterfly pattern of ejecta and an eventual elongated peak in the incoming end of the oval crater (Planetary Geology) . Tektites are part of the ejecta. The crater associated with the Australasian strewnfield has not yet been identified, but is presumed to be somewhere in Central Asia (Lo 2002).

The chemical composition and the age of tektites in the Australasian strewnfield are the same, indicating that they all originate from one and the same impact, see Table 1 (Giuli 2000).

“They were formed 780 ka ago. This is a mean based of 770 ka obtained using the 39Ar-40Ar technique (a few low values were discarded) by Izett and Obradovich (1992) (Izett 1992) and a stratigraphic age based on the placement of microtektites, 10 ka below the Brunhes -Matuyama magnetic-reversal boundary dated at 778 ka..” (Tauxe 1996)”. (Wasson 2003).

The form and surface features of Vietnamese splashform tektites have been investigated for more than hundred years. The prevailing theories suggest the forms primarily are created by rotation and spinning and that the surface sculpturing is created by ablation during fast movement through the atmosphere. Theories about chemical etching and spalling as the major creators of surface sculpturing have been proven unlikely.

Basic observations

From a collection of 1 ton of tektites found in the Dalat area in Vietnam, a sample of 203 tektites was investigated closely. The sample was selected based on the two major findings by Nininger H.H. and Huss G.I. (Nininger 1967) examining 50,000 tektites from Dalat :

1. Most indochinites are fractured.

2. Two tektites are buckled into the shape of a boomerang, leaving both parts joined together by the interior, which remained plastic at the time of fracture.

Other surface features like ablation, cracks, air bobble and stretching marks were selection criteria’s together with variations in forms from round to elongated, dumbbell and twisted shape to any ‘strange forms’.

One tektite showing interior plastic bending was found. Interestingly it has the same leguminous shape as the two found be H. H. Nininger and Huss. (Nininger 1967) . (Fig 1).

An additional four shells with unmistakable breaks and stretching of plastic interior were found. (Fig 1). The rest of the 203 tektites were divided into 3 groups based on their form: Shells showing distinctive breakage and a concave/convex form. Elongated forms like dumbbells, teardrops etc. Round forms from ball shape to disk and oval forms. (Fig 2).

Shells

Shells are characterised by having been parts of a larger now broken body. The shells are pieces of a tektite that was not all solidified on landing, still having a fluid or plastic/elastic interior. Upon impact this intermediate body cracks into a number of shells and the interior body, the nucleus, escapes due to its elasticity and becomes a tektite of its own, usually one of the round forms. The evidence for this is displayed by a number of observations: Shells show a layered structure with a coating layer on the inner concave side, a thicker solidified layer that cracks and a moderately plastic layer on the convex outer side evidenced by impact planes (Fig 3).

The shells come from intermediate bodies that had a round ball-like to a flat drop form evidenced by the form of the shells. One special abundant form has three to five edges with sharp up-going rounded angles. These shells come from the top of the intermediate body and are blown off on impact like a lid. Shells show none or only moderate ablation on the convex side (Fig. 2).

Fig. 3. Shell showing 3 layers, 1: Inside coating layer. 2: Solid layer. 3: Outside plastic layer. 4: Impact planes.

Fig. 4. Tektite (nucleus) with two impact points, one at the top, one at the bottom. Blue ring: Inward air bobble. Yellow lines: Air bobble tunnels

Elongated forms

The elongated forms are primarily dumbbells, teardrops, sticks and other irregular elongated forms. These forms can all be explained by fast rotation around 1, 2 or 3 axis of a fluid or plastic body. Teardrops are dumbbells broken during rotation or landing. Most characteristic is that these forms often have stretching marks on the surface and in the interior. Stretch marks are formed by two way opposite forces parallel to the stretching marks, typically from rotation, or as floating marks from gravity pull. The stretching process is documented by stretched air bobbles parallel to the stretching lines. (Fig 2, Table 2)

Round forms

The round forms are lighter primary bodies or nuclei that escaped due to elasticity when the intermediate form cracked on impact. The forms vary according to fluency, plasticity and elasticity and often has characteristic air bubble tunnels created during impact, between the shell and the nucleus. The air bubble tunnels are not cracks and are not formed by aerial ablation. They all have the same focal point from the impact. More than one set of tunnels can be found on some tektites. In case of more than one, two of them will often be in direct opposite directions (top and bottom). The bottom tunnels created by impact and the top tunnels from shedding off the lid. See illustrations (Fig 4).

Depending on the original form, plasticity and rotation, the end form of the nucleus can be onion shaped, double convex, flat, concave, double concave or oblate. Upon landing the plastic body is insulated on the bottom side, enabling re-melting and cavity creation from heated air underneath. This changes the bottom side structure to a more course concave central structure and a smooth circular basis around, compared with the top side’s finer and more uniform structure often with floating marks. (Fig 6).

Bodies with high viscosity and low plasticity remain round to double convex, high plasticity or fluid bodies end up as flat, concave or double concave tektites. Floating marks can show partial disappearance of tails from onion shaped bodies. Tails can also show craterlike cracking due to difference in contraction during solidification. Floating marks are often irregular like altitudes on a map.

Cracks are created by a parting of regions of the solid surface. With a plastic interior it can be documented by stretching marks across the crack. Cracks are often V formed, not straight and have a flat basin and individual cracks have a different focus. Air bubble tunnels are straight, same width all over, ‘O’ shaped basin and are focused at the same impact point.

Primary round bodies can show impact planes on the surface like shells, air bubble tunnels/cracks at the impact point and air bubbles with no or mild ablation. Due to erosion and fragmentation it is not always possible to classify a tektite as either primary or nucleus.

Fig. 5. Intermediate form cracks on impact into shells (Lid, bodies and impact points) and nucleus with air bobble tunnels, a. Low velocity P-waves from the impact point through the liquid/plastic nucleus and high velocity refraction waves in the solid shell, b. Reconstruction of intermediate body from impact shell, lid and nucleus tektites, c. Air bobble tunnels on the nucleus. Refraction waves can explain the upward round angle found on many lid edges. (Also see fig 2 and 6).

Fig. 6. Reshaping process. Reshaped nuclei according to viscosity and bottom reheating. Floating marks and air bobble tunnels.

Classification

Based on the previous observations, the tektites are classified into three classes based on creation and into a number of subclasses based on form. (Table 3).

To distinguish between primary forms and nuclei the main characteristics can be used, but for eroded tektites or fragments it may not always be possible as the nucleus may have more or less the same form as the intermediate body.

Creation

Illustrations of the formation of shell and nuclei Vietnamese tektites. (Fig 5, 6).

The thickness of the shells varies between 2 mm and 22 mm for 105 shells among the 203 tektites investigated. Any primary body with one or another dimension thicker than twice this length would have an elastic nucleus inside. All tektites above 75 grams to 294 grams were nuclei tektites. Primary forms like balls, dumbbells etc. were below 75 grams, showing that tektites with a plastic/liquid nucleus crack on impact leaving shells and a nucleus.

Conclusion

Based on the examination of 203 Vietnamese tektites a new classification has been established based on creation and form. The three creation classes, primaries, shells and nuclei can explain the great variety in forms as a result of a meteorite impact on Earth. The shells and nuclei are remnants of an intermediate form that cracked on impact. One tektite was found solidified as this intermediate form. This also explains the two observations in (Nininger1967) that most Vietnamese tektites are broken – they are mostly shells – and the two buckled tektites – they are intermediate forms. Differences in viscosity, plasticity and elasticity explain the form and sub form classes of nuclei tektites. Differences in rotation around 1, 2 or 3 axis explains the sub form classes of primary tektites.

References

GIULI G., PRATESI G., CORAZZA M.,1 AND CIPRIANI C. (2000) American Mineralogist 85, pages 1172–1174.

IZETT G.A AND OBRADOVICH J.D. (1992) Laser-fusion 40Ar/39Ar ages of Australasian tektites. In 23^rd Lunar and Planetary Science Conference, Lunar and Planetary Institute, Houston, pp. 593–594.

LO C-H., HOWARD K. T., CHUNG S-L. AND MEFFRE S. (2002) Laser fusion argon-40/argon-39 ages of Darwin impact glass. Meteorit. Planet. Sci. 37, 1555–1562.

NININGER H.H. AND HUSS G.I. (1967) Tektites that were partially plastic after completion of surface sculpturing. In: Barnes (edit.) Tektites (1973). Dowden, Hutchinson & Ross Inc., 249-250.

Planetary Geology ASTR 3C11 UCL, 2004-06-25, http://www.apl.ucl.ac.uk/lectures/3c11/impacts2.pdf

TAUXE L., HERBERT T., SHACKLETON N. J. AND KOK, Y. S. (1996) Astronomical calibration of the Matuyama Brunhes Boundary: consequences for magnetic remanence acquisition in marine carbonates and the Asian loess sequences. Earth Planet. Sci. Lett., 140, 133-146.

WASSON J. T. (2003) ASTROBIOLOGY, Volume 3, Number 1.

TABLE 1. Chemical composition (wt% oxides) of tektites

Note: Uncertainties (1s) in last decimal place shown in parentheses.

Tabulated data are averages of five individual analyses. (Giuli 2000)

	Indochinite	Thailandite	Philippinite	Cambodianite
SiO2	75.05(44)	79.00(48)	72.47(44)	72.50(44)
Al2O3	12.02(22)	10.15(20)	12.97(24)	13.25(24)
FeO	4.19(26)	3.58(26)	4.52(28)	4.69(30)
CaO	2.14(10)	1.15(8)	2.64(12)	1.69(8)
MgO	1.74(8)	1.38(8)	2.02(10)	1.84(10)
K2O	2.36(12)	2.39(10)	2.50(12)	2.54(12)
Na2O	1.23(16)	1.21(12)	1.46(18)	1.32(18)
TiO2	0.69(8)	0.56(8)	0.74(8)	0.75(8)
MnO	0.10(6)	0.11(6)	0.12(6)	0.10(6)
Total	99.52	99.53	99.44	98.68

Table 2: Illustration of spin form formation

Balls: Created automatically by surface tension in liquid bodies. No rotation. Have 3 axes. Circular: Created by rotation around 1 axis. Forces increase with distance from the center resulting in most mass at the edge (stretching at the center). Flat Dumbbell: Created by rotation around 2 axes. Slow rotation on second axis. Changing the circular to a flat dumbbell. Cylinder Dumbbell: Created by rotation around 2 axes. Changing the flat form to a cylinder. Forces increase with distance from the center, resulting in most mass at the edge and stretching at the centre. Twisted cylinder: Created by rotation around 3 axes. Only third rotation is shown.

Table 3: Vietnamese splash form tektite classification

Table 3: Vietnamese splash form tektite classification

Creation classes	Form classes	Sub Form classes
Primary: Created directly at meteor impact. Form changed from ball to flat dumbbell, cylindrical dumbbell over teardrops via 1 and 2 axis rotation. Twisted forms also rotate around the third axis. Main characteristics: Stretch marks on surface. Impact planes. Minor ablation.
	Balls	Ball Shaped
	Dumbbells	Flat/cylindrical, straight/twisted
	Teardrops (Clubs)	Flat/cylindrical, straight/twisted
	Sticks	Flat/cylindrical, straight/twisted
	Intermediate	Flat/cylindrical, straight/twisted
Shells: Created at impact of intermediate body splitting into shells and nuclei. Main characteristics: Convex sculptured side / concave smooth side.
	Lids	Number of edges 3-5
	Bodies	Flat/cylindrical, straight/twisted
	Impact point
Nuclei: Created at impact of intermediate body splitting into shells and nuclei Main characteristics: Air bobble tunnels, floating marks, tail.
	Balls	Ball shaped
	Ovals	Flat, convex, concave
	Onions	Have tail

Correspondence and request for material should be addressed to: edamgaard@hotmail.com

10-12 Nguyen Cong Hoan,

Hanoi, Vietnam