X-RAY ANALYSIS

Written By Aubrey Whymark 2011-2017
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.

Download the PDF version of 'X-Ray Larger Philippinites'

Bubbles in Large Philippinites

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Bubbles the norm in large Philippinites. Typically a number of smaller bubbles are present in breadcrusts, whereas larger smooth sphere yield a single larger bubble. Large spheres would have remained molten the longest, allowing for bubble amalgamation.
 
Cat No. 
No number
PB1117430
PB1117524
PB1117429
PM1115009
PB1111747
PB1115020
PB1117239
PB1115021
PB1115008
PB1117212
PB1113073

PB1111857
PB1117387
PB1111285
PB1117409
PB1113477
PB1117232
PB1117085
PX1117377
PX1117401
PB1117370
PB1117426
PB1117403
PB1113503
PB1117406
PB1112747
PB1117371
Weight (g)
 1194.80
 1018.40
 966.85
 865.11
 693.09
 656.47
 600.18
 551.26
 533.10
 459.18
 452.69
 412.58

 373.73 
 326.36
 318.93
 308.99
 281.95
 259.76
 257.81
 229.96
 226.04
 213.38
 209.89
 199.20
 171.40
 163.47
 156.70
 143.49
Type 
Smooth sphere 
Smooth sphere 
Smooth sphere 
Smooth sphere 
Smooth sphere 
Smooth - slightly grooved sphere 
Smooth sphere 
Smooth sphere 
Smooth sphere 
Smooth - slightly grooved sphere 
Grooved -smooth sphere 
Grooved sphere 

Grooved sphere 
Grooved breadcrust sphere 
Grooved breadcrust sphere 
Grooved breadcrust sphere
Grooved breadcrust sphere
Grooved breadcrust sphere
Grooved breadcrust sphere
Grooved breadcrust sphere
Grooved breadcrust sphere
Grooved breadcrust sphere
Grooved breadcrust sphere
Grooved breadcrust sphere
Grooved breadcrust sphere 
Grooved breadcrust sphere
Grooved breadcrust sphere
Grooved breadcrust sphere
Dimensions (mm)
 111x107x103
 103x93x82
 107x86x81
 90x85x83
 85x84x73
 90x88x83
 78x78x73
 79x74x72
 81x77x67
 74x72x68
 70x70x69
 76x74x59

 73x66x61
 67x65x62
 69x63x63
 65x65x62
 63x62x59
 66x63x56
 64x63x62
 61x60x59
 62x60x58
 60x60x60
 61x59x55
 61x60x52
 55x53x51
 60x56x53
 56x54x52
 57x53x48
Number of bubbles 
 1
 1
 1
 1
 2
 1
 1
 1
 1
 3 poorly defined
 3
 3 plus maybe 3 small

 Numerous >7
 4
 Numerous
 Numerous
 4
 4 plus
 3
 2-3
 Numerous
 Numerous
 Numerous >6
 1
 Approx. 8
 Numerous
 Approx. 9
 Numerous
Bubble dimensions (mm)
 70x73
 15x14
 14x12
 16x13
 13x12, 3x3
 59x57
 14x11
 12x10
 11x10
 2 to 7 mm diameter
 9x9, 5x5, 5x5
 10x10, 6x4, 5x5 plus 3 possible
1 to 2 mm diameter
 8x6, 6x5, 2 to 4 mm for remainder
 9x9, 2 to 5 mm for remainder
 1 to 5 mm diameter
 1 to 4 mm diameter
 2 to 7 mm diameter
 8x7, 3 to 5 mm for remainder
 2 to 7 mm diameter
 10x9, 5x4
 1 to 4 mm diameter
 7x7, 1 to 3 mm for remainder
 2 to 4 mm diameter
 17x14
 2 to 4 mm diameter
 1 to 5 mm diameter
 2 to 5 mm diameter
 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.

Bubble Abstract

​In 2015, the author of this site co-authored an abstract with Krauss and Kloess titled 'X-RAY COMPUTED TOMOGRAPHY OF BUBBLE-CORED TEKTITES'.
Link to Bubble Abstract
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.

Update

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. 
No number
No number
PB1117430
No number
PB1117524
Weight (g)
 1281.89
 1194.80
 1018.40
 995.10
 966.85
Type 
Smooth sphere 
Smooth sphere 
Smooth sphere 
Smooth sphere 
Smooth sphere 
Dimensions (mm)
 105x102x101
 111x107x103
 103x93x82
 96x91x85
 107x86x81
Number of bubbles 
 1
 1
 1
 1
 1
Bubble dimensions (mm)
 61x60
 72x71
 15x15
 15x15
 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

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.