The primary tektite morphology should be defined as the initial shape of the tektite, formed by disruption of the melt and defined by cohesive and centrifugal forces, prior to interaction with the atmosphere and exposure to aerodynamic forces. One can think of these morphologies as equivalent to those formed in a vacuum such as space.

As we shall see, however, tektites were not typically formed in a total vacuum and thus the primary morphology must be artificially differentiated from the contemporaneous and subsequent aerodynamic modifications (as applicable). The aerodynamic influence on the molten primary body will be to a greater or lesser extent dependent on density of the atmosphere and velocity of the tektite vs. cohesive forces (surface tension), which increases with viscosity. The traditional view, based on australites, that primary morphologies form, then cool, then re-enter, ablate and spall is somewhat over-simplistic in approach.

Two schools of thought exist with regards primary shape formation, and indeed what actually constitutes a primary shape is questioned. This results in some degree of overlap with the subsequent plastic deformation chapter in terms of initial explanation.

Prior to discussion, a couple of terms must be defined for the purpose of this page as there are differing definitions available in the literature. In studying the formation of primary morphologies centrifugal forces versus cohesive forces (surface tension) is of principal interest. Centrifugal forces arise by rotation. A body has 3 axes of rotation, which have already been discussed: Roll, pitch and yaw. With reference to Elkins-Tanton et al. (2003) 'rolling' is defined as rotation about a single axis (the yaw axis in this case), also termed axisymmetric rotation. This compares with 'tumbling', which is defined as rotation about more than one axis (i.e. rotation about 2 or 3 axes), also termed non-axisymmetric rotation. The absolute and relative velocity of rotation about the different axes will define the morphology by creating centrifugal forces and instabilities that act against cohesive forces (surface tension). These forces are defined below:

ABOVE: Various forces acting upon a molten tektite globule. A) Cohesive forces (surface tension) try to maintain a spherical body. The body will be spherical in the absence of other significant forces (JRank Article 1182). B) In a dumbbell or biconcave disc cohesive forces attempt to form spherical shapes (via an apioid) or spheroidal cross sections, respectively. C) A tumbling motion of a molten body will result in a spherical form as cohesive forces dominate. D) A rolling motion will result in  flattened oblate spheroid, disc, biconcave disc (shown) and tori due to centrifugal forces exceeding cohesive forces (Elkins-Tanton et al., 2003; Stauffer and Butler, 2010). E) If this rotating biconcave disc then tumbles a dumbbell will form. If a biconvex form formed by rotation then tumbles a prolate body will form, such as a rod or bar (Elkins-Tanton et al., 2003; Stauffer and Butler, 2010). F) Stationary, on a solid surface or in flight acting against other aerodynamic forces, the molten body will flatten out due to hydrostatic pressure (McDonald, 1954). G) The body will also flatten out due to deceleration pressure. This can arise during atmospheric exit and re-entry (if molten) (Chapman, 1964). H) Aerodynamic forces have the highest pressure at the stagnation point, in the centre of the anterior (McDonald, 1954) causing an inward bowing termed a 'punt'. I) Aerodynamic forces - shear forces between the air and molten tektite may set up vortices within a tektite (after Baumann et al., 1992). J) These vortices would ultimately lead to biconcave discs and then unstable tori (after Baumann et al., 1992).

In the proximal setting we observe spheroidal, ellipsoidal, biconvex, plano-convex, concavo-convex, biconcave forms and toroidal fragments. All of these forms can be derived from aerodynamic forces acting on a body. The rolling mechanism, on the other hand, does not account for plano-convex forms or concavo-convex forms, unless these very common forms are considered imperfections of the rarer biconcave morphology. A combination of rolling, followed by aerodynamic forces could be used to account for these morphologies.

Next, if we look at medial and distal tektites a problem is encountered. Distal forms are off-spherical to ellipsoidal re-entry bodies. Or, taking the traditional view (which does not account for their orientation), they were mainly spherical bodies. Medial bodies can be readily measured. The vast majority of medial forms were flattened spheres: Ellipsoidal to perhaps biconvex forms. Rarer medial tektites were perfect spheres and had no orientation during re-entry. The absence of the more flattened bodies, such as concavo-convex, biconcave and toroidal bodies  is enlightening. Spheroidal dumbbells are not uncommon in these medial assemblages, yet these are believed to be derived from the biconcave, centrally thinned, bodies (Elkins-Tanton et al., 2003; Stauffer and Butler, 2010). One also observes occassional non-saddled prolate forms which supposedly evolved from discoidal forms. So, by this mechanism, every single biconcave form, without fail, formed a dumbbell, yet most discoidal forms failed to evolve to prolate forms. Why are centrally thinned, supposedly transitional, bodies never found in the assemblage? It could be argued that the longer liquid life and lower stability of these bodies might account for their total absence. Another, perhaps more feasible argument, is that these biconcave/toroidal forms are not genuine primary morphologies. That is why biconcave/toroidal forms only occur in the proximal setting where bodies formed at lower altitude and consequently aerodynamic forces would have been significantly higher. If one assumes aerodynamic forces acted on these bodies then it must also be applied to other bodies.

Furthermore, there are unstable morphologies that are produced by the rolling mechanism. These include 3, 4, 5, and 6 lobed forms (Tagg et al. 1980; Aussillous and Quéré, 2004; Heine, 2006; Hills and Eaves, 2008; Lü et al., 2010). As the number of lobes increases, so does instability (Lü et al., 2010) and Elkins-Tanton et al. (2003) considered all multi-lobed (3+ lobe) forms unstable. Multi-lobed forms are never observed in tektites.

Flattened teardrops present a further problem. Dumbbells have been demonstrated to be produced by a rolling motion creating a centrally thinned disc, followed by a tumbling motion to create a dumbbell. Teardrops are derived from the splitting apart of dumbbells at higher speeds of rotation. Teardrops are end forms in the rolling and tumbling model. What we observe, however, is a full sequence of spheroidal, ellipsoidal, biconvex, plano-convex, concavo-convex and biconcave teardrops, indentical to the spherical-disc sequence.

In these flattened teardrops the tails cooled the quickest, whilst the bulbous ends took longer to cool and therefore suffered greater deformation. The positioning of the tails is random and can be anywhere from central, as in the case of ‘Hershey’s Kisses’, or to the side, but always swept towards the posterior. Tails have not been ‘spun’ to the sides of the discs, implying a lack of centrifugal forces. Commonly tektites have undergone some degree of etching. This allows us to study the external expression of the internal schlieren or flow lines. The internal flow lines around the tail probably formed as the parent dumbbell split in two. Some teardrops clearly exhibit ‘spinning’ whilst in many the spiraling of flow lines appears to be minimal.

Teardrops present a clear problem to the rolling and tumbling mechanism, hence the lack of explanation in the literature. In this mechanism the initial rolling motion, which created a biconcave disc, must have become tumbling to produce a dumbbell and then returned to rolling to produce a flattened teardrop. Even this improbable sequence of events fails to explain all the morphologies and fails to explain the positioning of the tail and why the tail is always swept to the posterior. Aerodynamic forces explain all observations.

In the proximal setting and very rarely in the medial setting (although not nearly as well developed) we see arciform or distorted/bent teardrops and dumbbells. In teardrops the tail is always swept to the posterior. In dumbbells the two lobes often bend towards the anterior with an arc, equivalent to a concavity or ‘punt’ in a disc, developed over the anterior. Effectively ‘open’ convex on the posterior and ‘open’ concave on the anterior. These morphologies appear to be problematic to obtain by means other than aerodynamic. These forms cannot be attributed to ‘freak’ bending whilst splitting, they follow clear and repeatable patterns.

The australites were the first formed tektites, ejected with the highest inherited velocities and highest melt temperature, disrupted at high atmospheric levels (reducing conductive cooling). The long liquid life allowed australites to cascade into smaller bodies, presumably as the melt droplets interacted with the highest reaches of the atmosphere during ejection. Consequently, australites are predominantly small forms that originally had predominantly spherical shapes. Teardrops and dumbbells are relatively rare.

Philippinites are intermediate between the australites and indochinites, but in terms of primary shapes they tend to be medium to large in size and typically originally spherical, with non-spherical primary forms making up only a small percentage of specimens. Dumbbells are not common, but not unusual, whereas true teardrops are exceedingly rare in philippinite collections. Again, this is attributable to the melt being relatively high temperature and being ejected with a relatively high velocity and an angle that allowed philippinites to form at high atmospheric levels, with a small part of the assemblage effectively forming in  ‘space’. The larger size of philippinites, when compared to australites, is probably attributable to a slightly more viscous lower temperature melt, that traversed the atmosphere (which acts upon the melt droplet) quicker due to a higher ejection angle and still reasonable velocity.

Elongated forms, dumbbells and (often very elongated) teardrops are found in abundance in Indochina, sensu lato. This is typical of a low temperature, viscous melt. Transient, non-equilibrium, morphologies, such as teardrops, are ‘locked-in’ as the tektite cools and surface tensions of the very viscous melt resist the external forces. For many indochinites the primary morphology was a transient phase. Atmospheric interactions immediately distorted the morphology into flattened discs and onion-forms. It could be argued that the morphologies that are distorted by atmospheric interaction are also primary morphologies as they formed whilst molten, but it is simpler to describe alterations to the tektite by atmospheric interaction as secondary plastic deformation modifications to the basic primary tektite shapes.

In the distal and medial realms most tektite morphologies can easily be assigned to an original primary or slightly plastically deformed primary form. Some fragments may be indistinguishable due to weathering and transportation processes. In the proximal setting one can identify plastically deformed primary morphologies. One can also identify amorphous blocky layered Muong Nong-type impact glasses. These layered forms represent the most viscous, lowest temperature melts. They are incompletely homogenised and may contain relict crystal grains. These bodies were too viscous to form discrete tektite droplets and can effectively be considered as ‘collapsed’ parts of the impact melt sheet.

Less discussed, are the array of indochinites between the perfect, often plastically deformed, primary morphologies (see Figure 7.6) and the blocky amorphous Muong Nong-type layered impact glasses (see Figures 7.9 and 7.10). Often only perfect morphologies make it into collections. In the Indochinese area many imperfect, often bubble-rich, forms exist (see Figures 7.7 and 7.8). The glass is fully melted and homogenised tektitic glass, but the spherical morphologies have failed to form (see Figure 7.8). These specimens are akin to the 35 poise (viscous melt) forms in the top left of Figure 7.5. These bodies represent disruption of the melt sheet, but at lower energy levels. The lower temperature melt is solidifying before it even moves towards an equilibrium form.

These assemblages with amorphous bubble-rich tektites (often with large circular bubbles or many elongate ‘stretched’ bubbles - see Figures 7.7 and 7.8) and twisted and contorted forms are indicative of proximity to the source crater. Similar forms can be found from the unrelated 1.2 km diameter Mt Darwin Crater in Tasmania, Australia, and 14 km diameter Zhamanshin Crater in Kazakhstan. The ejecta from these impacts is characterised by layered impactites, bubble-rich forms, specimens with stretched bubbles, commonly contorted forms and rare small splashform type impactites that grade towards true tektites. Similar proximal ejecta is found in the Central European 'Moldavite' strewn field.

The unshaped tektites of Muong Nong (note that Muong, meaning town/district, is also variously spelt Mouang, Muoang, Muang, Mueang and Mong, with Muang appearing to be the correct spelling in Laos), were first described by Lacroix (1935). The term Muong Nong-type tektite was popularised by Barnes (1961). In this website the term Muong Nong-type layered impact glass is favoured for the same (maintaining the usage of the historic Muong Nong term). Muong Nong-type layered impact glass is transitional and genetically linked to 'splash-form' tektites: Chemically they are very similar. The key difference is that Muong Nong-type layered impact glass '...seem to have experienced a lower peak temperature and pressure, thus preserving the precursor material much better than the splash forms do' (Koeberl, 1986).

Muong Nong-type layered impact glasses are typically blocky. Fiske (1996) decribes large fragments as being surrounded by smaller ones. Larger fragments fit together whilst smaller fragments have one major fracture surface and were probably exfoliated from the larger block. Fragments he studied appeared to be 'potato'-like blocks when reconstructed and not flat puddles. Alternating dark (silica-rich) and light (reduced silica) layers are seen in Muong Nong-type layered impact glasses (Koeberl, 1985).

Koeberl (1992) identifies the key differences between Muong Nong-type layered impact glasses and splash-form tektites as '1) higher concentrations of volatile elements (e.g. Cl, Br, Zn, Cu, Pb); 2) chemically inhomogenous on a millimeter scale; 3) having dark and light layers with different chemical compositions; 4) may contain relict mineral inclusions; 5) large and more abundant bubbles; 6) large and irregular size'.

Within the Australasian strewn field Muong Nong-type layered impact glasses are found in mid-southern Laos, eastern Thailand, mid-southern Vietnam, northern Cambodia and Hainan, with the odd occurrence in northern Laos and northern Vietnam. The area typified by the Muong Nong locality in Savannakhet Province, but inclusive of a larger area in southern Laos and the southern part of eastern Thailand is dominated by these Muong Nong-type layered impact glasses in the absence or near absence of splashform tektites (Schnetzler,1992; Schnetzler and McHone, 1996). Trnka (pers. comm., 2013), however, informs the author that splashform tektites can be found across this area alongside Muong Nong-type impact glass. Schnetzler (1992) and Schnetzler and McHone (1996) offer an excellent overview of the distribution pattern and are well worth refering to in this discussion.