X-Ray Analysis

Following the first set of x-rays I returned to get more data. I mainly concentrated on larger Philippinites (breadcrusts, grooved spheres and smooth spheres). I also x-rayed more Indochinite dumbells. Here are my x-rays for the larger philippinites from visit 1 and 2.

ABOVE: A slide show of x-rayed larger tektites. Note that images are not to scale.

 

Cat No. 

Weight (g)

Type 

Dimensions (mm)

Number of bubbles 

Bubble dimensions (mm)

 No number 1194.80Smooth sphere  111x107x103 1 70x73
PB1117430 1018.40Smooth sphere  103x93x82 1 15x14
PB1117524 966.85Smooth sphere  107x86x81 1 14x12
PB1117429 865.11Smooth sphere  90x85x83 1 16x13
PM1115009 693.09Smooth sphere  85x84x73

 2

 13x12, 3x3
PB1111747 656.47Smooth - slightly grooved sphere  90x88x83 1 59x57
PB1115020 600.18Smooth sphere  78x78x73 1 14x11
PB1117239 551.26Smooth sphere  79x74x72 1 12x10
PB1115021 533.10Smooth sphere  81x77x67 1 11x10
PB1115008 459.18Smooth - slightly grooved sphere  74x72x68 3 poorly defined 2 to 7 mm diameter
PB1117212 452.69Grooved -smooth sphere  70x70x69 3 9x9, 5x5, 5x5
PB1113073 412.58Grooved sphere  76x74x59 3 plus maybe 3 small 10x10, 6x4, 5x5 plus 3 possible 1 to 2 mm diameter
PB1111857 373.73 Grooved sphere  73x66x61 Numerous >7 8x6, 6x5, 2 to 4 mm for remainder
PB1117387 326.36Grooved breadcrust sphere  67x65x62 4 9x9, 2 to 5 mm for remainder
PB1111285 318.93Grooved breadcrust sphere  69x63x63 Numerous 1 to 5 mm diameter
PB1117409 308.99Grooved breadcrust sphere 65x65x62 Numerous 1 to 4 mm diameter
PB1113477 281.95Grooved breadcrust sphere 63x62x59 4 2 to 7 mm diameter
PB1117232 259.76Grooved breadcrust sphere 66x63x56 4 plus 8x7, 3 to 5 mm for remainder
PB1117085 257.81Grooved breadcrust sphere 64x63x62 3 2 to 7 mm diameter
PX1117377 229.96Grooved breadcrust sphere 61x60x59 2-3 10x9, 5x4
PX1117401 226.04Grooved breadcrust sphere 62x60x58 Numerous 1 to 4 mm diameter
PB1117370 213.38Grooved breadcrust sphere 60x60x60 Numerous 7x7, 1 to 3 mm for remainder
PB1117426 209.89Grooved breadcrust sphere 61x59x55 Numerous >6 2 to 4 mm diameter
PB1117403 199.20Grooved breadcrust sphere 61x60x52 1 17x14
PB1113503 171.40Grooved breadcrust sphere  55x53x51 Approx. 8 2 to 4 mm diameter
PB1117406 163.47Grooved breadcrust sphere 60x56x53 Numerous 1 to 5 mm diameter
PB1112747 156.70Grooved breadcrust sphere 56x54x52 Approx. 9 2 to 5 mm diameter
PB1117371 143.49Grooved breadcrust sphere 57x53x48 Numerous 1 to 5 mm diameter

ABOVE: A table of x-rayed philippinites and interpreted number of bubbles and bubble dimensions.

Method:

I used an older x-ray machine with a photographic plate onto which the specimens were placed. It was necessary to image the specimens at different powers/factors in order to pick up the bubbles. If the power/factor was too high or too low in relation to the thickness of the tektite glass then the bubble was not observed. (Too high and the plate is black, too low and the whole of the specimen is white). The bubble dimensions obtained may be slightly larger than the actual bubble size (maybe up to 5% as a very rough estimate) because the x-rays project onto a photographic plate below from a smaller area above - so it is like seeing a shadow from a single light source above.

I used 28 large philippinites, predominantly from Paracale, Bicol, Philippines, 1 from Masbate and 2 from unknown localities (likely Bicol). Aside from the two spheres with known large bubbles (1,194.80g and PB1111747) the specimens were picked randomly, trying to get a representative variety of sizes. The smallest, more typical, philippinites were not analysed. Specimens were taken from breadcrust spheres, grooved spheres and smooth spheres.

Results:

Firstly the reader  should be aware that the photographic plates against a light table (you can also use a brightly lit blank computer monitor) are of a much higher resolution than what I was able to reproduce by scanning and photographing these plates. The presented images do, however, give a good impression of what I have seen. Within the limited database some clear trends were identified.

Specimens over 500g typically contained one 'large' bubble around 10-15 mm diameter, near to slightly off spherical. Typically this bubble was in the centre, or close to the centre, of the specimen (note that on the image the white part is the thickest/central part of the sphere and the margin/border is in the black area and can often only be picked up on a light table). Specimens in this size range are typically smooth spheres.

Roughly from 500 to 320g there was a trend of one 'medium' sized bubble and a couple of smaller bubbles, often 3 bubbles in total. The largest bubble was typically 7-10 mm in diameter and spherical or close to spherical. The bubbles were located randomly in the central portion of the tektite. Specimens in this size range are typically grooved spheres.

Below 320g the tektites were typified by bubble complexes, or numerous smaller bubbles, often 2 to 5 mm in diameter and spherical or close to spherical. Some larger bubbles are observed. The boundary between the 500-320 g and below 320g sub-sets is somewhat blurred and is more of a trend, but there does appear to be a valid subdivision. The bubble complexes were located in the central portion of the tektite. Specimens below 320g are typically breadcrust spheres.

ABOVE: A summary page of x-rayed larger philippinites. Please view the powerpoint presentation above for more details.

Discussion:

It is considered that, for the most part, the majority of bubbles were identified. The larger specimen PM1115009 (693.09g) exhibits both a large and a small bubble, which gives confidence that had smaller bubbles existed in other large specimens then they should also have been identified. The absence of small bubbles in the larger spheres is not considered a problem related to the power/factor and is likely genuine. 

It is probable that in larger spheres the stability of the glass sphere is increased by the presence of a bubble and therefore there may be a bias in nature, with spheres that contain bubbles surviving until today whilst spheres containing no/smaller bubbles may have fragmented. This may be true to some extent (particularly when a large bubble is present), but the consistency of bubbles would suggest this is a genuine primary trend.

Bubbles are fairly centrally placed as the tektite cooled from the outside-in.

The presence of a single large bubble in the large smooth spheres as oppose to numerous smaller bubbles in the smaller breadcrust spheres may be a reflection of cooling times. The smaller spheres cooled quicker, trapping the smaller bubbles in place before they reached their optimum configuration (1 bubble). The larger spheres would have cooled slower, probably allowing sufficient time for the smaller bubbles to merge into a single large bubble.

In these spherical philippinites the bubbles are typically spherical to very slightly ellipsoidal. The fact that the bubbles are close to spherical, even in the largest specimen, adds weight that when these tektites re-entered the atmosphere they had a hard and brittle exterior which resisted plastic deformation, which would have in turn distorted the bubbles. Philippinites re-entered the atmosphere with a solid and brittle exterior.

Contrary to popular myth, tektite glass is not bubble free. In fact in these larger specimens bubbles are the 'norm' and it would be unusual to find a 100% solid sphere.

 

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Brief update on 19 September 2011. I have now obtained and x-rayed a couple more large specimens (1281.89g and 995.10g), alongside 3 previously x-rayed specimens. The measurements on the previous 3 specimens differ very slightly in these images. Previous conclusions are supported by these two additional specimens.

Cat No. 

Weight (g)

Type 

Dimensions (mm)

Number of bubbles 

Bubble dimensions (mm)

No number 1281.89Smooth sphere  105x102x101 1 61x60
No number 1194.80Smooth sphere  111x107x103 1 72x71
PB1117430 1018.40Smooth sphere  103x93x82 1 15x15
No number 995.10Smooth sphere  96x91x85 1 15x15
PB1117524 966.85Smooth sphere  107x86x81 1 14x14

ABOVE LEFT: The 1,194.80g specimen        ABOVE RIGHT: The 1,281.89g specimen

 ABOVE LEFT: 966.85g         ABOVE MIDDLE: 995.10g         ABOVE RIGHT: 1018.40g

 

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Study of Dumbbells:

As an aside, I wanted to test whether asymmetrical dumbbells typically contained a bubble in the bulbous end. Whilst I worked on a very limited database (8 additional indochinite specimens on top of 4 indochinite and 1 philippinite dumbbells previously x-rayed), I could find no evidence that this was the case. The asymmetrical bulbous ends mainly comprises glass and not bubbles, so I do not believe bubbles significantly influence the asymmetry of dumbbells.

ABOVE: A selection of Indochinites x-rayed at different powers/factors. No large bubbles were revealed in these specimens.

  

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