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Lechatelierite in Moldavite Tektites: New
Analyses of Composition
Martin Molnár1, Stanislav Šlang2, Karel Ventura3. Kord Ernstson4.
1Resselovo nám. 76, Chrudim 537 01, Czech Republic (molnar@ego93.com) 2Center
of Materials and Nanotechnologies, University of Pardubice, 532 10 Pardubice, Czech
Republic, stanislav.slang@upce.cz 3Faculty of Chemical Technology, University of
Pardubice, 530 02 Pardubice, Czech Republic, karel.ventura@upce.cz. 4University of
Würzburg, D-97074 Würzburg, Deutschland (kernstson@ernstson.de)
ENTER NAMES OF AFFILIATED INSTITUTIONS
PRESENTED AT:
INTRODUCTION
Moldavites are tektites with a beautiful, mostly green discoloration and a very pronounced sculpture (Fig.1),
which have been studied many times e.g. [1-3]).
Fig. 1. Moldavites from Besednice analyzed in this study. Scale bar 1 cm.
According to the most probable theory, they were formed 14.5 million years ago together with the Ries crater
meteorite impact (http://www.impact-structures.com/meteorite-impact-germany/the-ries-impact-structure-
germany/)in Germany. They belong to the mid-European tektite strewn field and fell mostly in Bohemia. The
prominent sculpture is considered the result of acidic waters in the ground having etched away the more alkaline
parts of the moldavite and left lechatelierite inclusions as sharp edges and peaks. Originally, the curious pitting
and wrinkles on the surfaces were compared to meteorite regmaglypts and the moldavites ascribed to a cosmic,
meteorite origin (F.E. Suess 1900). Lechatelierite (https://en.wikipedia.org/wiki/Lechatelierite) is amorphous
SiO silica glass and commonly forms at very high temperatures in lightning strike fulgurites and as a result of
shock metamorphism during meteorite impact cratering. Authors [4, 5] state that it is 99% SiO - based. A
comparison reveals (Tab. 1):
Tab.1. Selected physical properties of pure SiO glass, lechatelierite and moldavite. Sources [5-7].
While refractive index and density are very close to each other, the main difference lies in the temperatures of the
softening point, which differs by more than 400 °C. This led to the question what is it that reduces the melting
point so rigidly and increases acid resistance.
The conclusion from the present comparison is clear. Lechatelierite from moldavite is not a pure SiO glass. Here
we report on experimental investigations that pursue this question and lead to new findings of the lechatelierite
composition.
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EXPERIMENTS AND RESULTS
Experiments 1 and 2 - the boron question. The question of lowering the melting point and acid resistance led
to the possibility of adding boron. The experiment 1 on a moldavite plate etched in 15%-HF to expose the
lechatelierite was performed by laser ablation spectrometry and showed B O concentration of >1%. In
experiment 2, 38 g of lechatelierite fragments were then separated from 482 g of pure moldavite, and after the
boron content remained high (Tab. 2), the remaining carbon was washed away. The analysis in Tab. 3 shows
remaining low boron content, which is obviously bound to the carbon of the moldavites [8].
Experiment 3 - EDS analysis of lechatelierite and embedding moldavite matter. In the SEM image of Fig. 2
measuring points and areas for EDS analyses have been marked, and the results for comparison are shown in Tab
4.
Fig. 2. SEM image of a carbon-coated moldavite specimen with marked measuring points in the area of
the lamellae and the surrounding material.
The results show that the composition of the lamellae differs significantly from the surrounding moldavite. The
moldavite material consists of SiO with traces of Al, Mg, Na, K, Ca, Fe and in places a small amount of Ti. In
the area of the lamellae the content of accompanying elements is significantly lower (close to the quantitative
error limit of this method. Particularly significant in comparison is the high silicon content with an average Si:O
ratio of 1.2 (0.42 in moldavite).
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Tab. 4. Results of the elementary EDS analysis of the carbon-coated moldavite specimen, mean values.
Lech = Lechatelierite lamellae, 6 samples; Mold = moldavite material, 5 samples.
Experiment 4 - the condensation beaker method and the SiO question. A fireclay graphite beaker was filled
with 20 g of concentrate of lechatelierite, which close together with an identical empty beaker was heated in a
maximum sealed electric furnace for 1 hour to a temperature of 1670°C (Fig. 3). After spontaneous cooling until
the next day, the previously empty cup was lined with a white felted mass (Fig. 3), which was analyzed in the
SEM (LYRA 3, Tescan) (Fig. 4).
For comparison we carried out a blind test with 20 g gravelly SiO sand from the Střeleč quarry and with exactly
the same experimental procedure of heating and cooling. After removal of the empty beaker, it did not even
contain traces of a felt mass (Fig. 3).
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Fig. 3. Condensation beaker after the lechatelierite experiment (left), condensation beaker after the Střeleč
sand experiment (reight), and experimental arrangement of the beakers in the CLASIC furnace (top).
Fig. 4. SEM images of the felted material in increasing magnification.
DISCUSSION AND CONCLUSIONS
The experiments no. 1 and no. 2 excluded basic concentrations of light elements in lechatelierite, i.e. lithium,
boron and beryllium. An interesting secondary finding was the fact that carbon inclusions in the moldavite
contain up to 1.7% boron.
Experiment no. 3 showed that lechatelierite consists mainly of silicon and oxygen atoms. The molecular ratio of
these elements is close to 1:1, which could indicate the presence of silicon monoxide (SiO). Silicon monoxide
[e.g., 6] is a diatomic molecule in the gaseous state. It is the most common silicon oxide in space [7]. In the
terrestrial environment, silicon monoxide forms a polymer (SiO)n, where n can be 2, 3, 4 or 5. The polymer
forms closed circular structures. It is self-igniting and reacts with water. The melting point is 1,702 °C and the
boiling point 1,880 ºC. Due to the stability of lechatelierite it is therefore unlikely that it consists only of SiO
glass. The ratio of Si:O = 1:1 can also be obtained by mixing silicon with silicon dioxide. This mixture reacts
above 1,650 ºC to form silicon monoxide SiO, which is volatile. This was confirmed by our condensation beaker
method, where at a temperature of 1,670 ºC gaseous SiO escaped from the lechatelierite concentrate and
condensed in the other beaker and oxidized to the characteristic SiO fibers (Fig. 4). A blind test with pure SiO
under the same conditions proved that it is not substantially volatile and does not produce felted fibers in the
accompanying beaker.
Conclusions
We suggest that lechatelierite consists of a mixture of SiO glasses and Si glass (pure silicon). We attribute to this
mixture the excellent acid resistance and, thanks to the eutectic of Si, SiO , the strongly reduced softening point
of 1.175 °C of lechatelierite.
References
[1] Skála, R. et al (2016) J. Geosciences, 61, 171-191. [2] V. Bouška, V. (1994) Moldavites. The Czech Tektites. Stylizace, Prag.
[3] Trnka, M. and Houzar, S. (2002). Bulletin of the Czech Geological Survey, 77, 283– 302. [4] Kučera, J. and Knobloch, V.
(1982) Radiochemical and Radioanalytical Letters, 54, 197-208. [5] Řanda, Z. et al. (2208) Meteoritics & Planetary Science, 43,
461–477. [6] Hohl, A. (2003) Untersuchungen zur Struktur von amorphem Siliziummonoxid. PhD thesis (in German),
Darmstadt, Technical University. Jutzi, P. and Schubert, U. (2003) Silicon chemistry: from the atom to extended systems. Wiley-
VCH.
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