The hypothesis that a part of the lechatellierites which originated by etching from a basic moldavite mass became broken off after deposition of moldavite in the sedimentation layer is advanced. Those found close to the original moldavite were measured for statistical averaging of length. The average length of lechatelierite fibers per cubic mm of moldavite mass volume was determined by measurement under a microscope in toluene. The data were used to calculate the depth of the moldavite layer that had to be etched to produce the corresponding amount of lechatelierite fragments. The calculations from five "fields" of moldavite surface, where layers of fixed lechatelierite fragments were preserved, produced values of 2.0, 3.1, 3.5, 3.9 and 4.5. Due to inadvertent loss of some fragments the determined values are somewhat lower than those found in references. The difference may be explained by the fact that the depth of the layer is only that caused by etching after moldavite deposition

Knobloch, V.

Knoblochova, Z.

Urbanec, Z.

English

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^i
w
Translation of "Leptani vltavinu v prirodnich podminkach", Casopis
Narodniho muzea v Praze, Rada prirodovedna, Vol. 149, No. 3-4, 1980,
pp. 140-144.
(NASA-TH-77334) ETCHISG OF ACLDAVISI ES
	 M84-15014
UNDER NATURAL CONDITICIS (National
Aeronautics and Space Administration) 10 p
HC A02/8F A01	 C SCL 03B	 Unclas
63/91 42783
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON, D.C. 20546
	 MARCH 1983
i
ORIGWAL PAGE r8
OF POOR QUALITY	
STANDARD TITLE PAGE
1. 
R rt aIM-77334 P. 
Ge^amm•nt Accession Me. > Recipient's Catalog No.
4. Title end subtitle S. Report Date
March 1983
ETCHING ' OF MOLDAViTES UNDER NATURAL 4. Performing organization Coda
CONDITIONS
7. Auther(s) 	 V.	 Knobloch,	 Z.	 Knoblochova, 8. Performing Organisation Report No.
Z.	 Urbanec-
10. work unit No.
9. Performing Organi lotion Nome and Address 11. Contrast U; C-!-nt No.
Leo Kanner Associates, NAS'W— 3541
13. Type of Report and Period LevaredRedwood City, CA 94063
Translation
12. Sponsoring Agency Nome and Address'
National Aeronautics and Space
td. Sponsoring Agency CodeAdministration, Washington, D.C. 20546
15. Supplementary Notes
Translation of "Leptani vltovinu v prirodnich podminkoch", Casopis Narodniho
muzea v Praze, Roda pri rodovedna, W . '49, No. 3 - 4, 1980, pp. 140 - 144.
16. Abstract
	 The paper advances the hypothesis that a -part of the
lechatelierites which originated by etching from a basic
moldavite mass became broken off after deposition of moldavite
in the sedimentation layer. 	 Those found close to the original
moldavite•.were measured for statistical averaging of length.
The average length of lechatelierite fibers per cubic mm
of moldavite mass volume was determined by measurement under
a microscope in toluene.	 The data were used to calculate the
depth of the moldavite layer that had to be etched to produce
the corresponding amount-of lechatelierite fragments. 	 The
calculations.from five "fields" of moldavite surface, where
layers'of fixed lechatelierite fragments were preserved, pro-
duced values Qf	 2.0,'3.1,	 3.5,	 3.9 and 4.5.
Due to inadvertent loss of some fragments the determined
,values are somewhat lower than those found in references. 	 The
difference may bE: explained by the fact that •the •depth of the
layer is only that :aused , by etching after moldavite depositio
17. Key words (Selected by Author(s)) 18. Distribution Statement
Unclassified - Unlimited
19.	 Security Clessif. (of this report) 20.	 security Clossif. (ol this page) 21. No. of Pages 27.
Unclassified Unclascified 8
G7
ETCHING OF MOLDAVITES UNDER NATURAL CONDITIONS
V. Knobloch, Z. Knoblochova, Z. Urbanec#
In comparison to tektites that are relatively young (such as /7.40*
e.g., australites and tektites of southeastern Asia), in which their
original surface became well preserved under favorable conditions
(O'Keefe 1967), in the case of old tektites--among which we may in-
clude moldavites--determination of their original shape and dimen-
sions which they had upon impact on the surface of the Earth is very
difficult.
4
1
k
During the course of millions of years such tektites underwent,
on the one hand, a more or less extensive transport and the resultant
abrasion, while, on the other hand, they were obviously exposed to
the effects of weathering and etching the extent of which can be de-
termined only with difficulty.
i
Effects of	 etching(1911) already pointed out by Jezek 
and Rosicky (1939) in connection with the problem of the origins of
sculpturing.
On the basis of optical properties of moldavite from Locenice
detected during observation in polarized light, Rost (1967) reached
the conclusion that loss of surface layers due to corrosion ranges
between 3-6 mm.
New findings relevant to the problem of etching resulted from
laboratory experiments of Kellner and Huang (1971) who studied ex-
tractive dissolution of individual elements from the surface layers
of masses of moldavite and of obsidian for a period of 21 days.
*Numbers in the margin indicate pagination in the foreign text.
0 Mathematics - Physics Facility, Karlevy University, Progue
1
t^
The results of the study made by Keller and Huang in regards to
etching of natural glasses (1971) essentially coincide with a person-
al communication by Vojtech regarding his experimental results ob-
tained in dissolution of synthetic and natural glasses, as well as
with the concept regarding the mechanism of damage caused to glass
by aquous media (Weyl 1938, Hlavacova 1964, Kaller 1957, Keppeler
1934, Berger 1936).
According to these concepts, the formation of glass is partici-
pated in, on the one hand, by a solid bond between silicon and oxygen
atoms Si-O-Si which forms the basic tetrahedral unit of ions SiO4- in
the glass structure and, on the other hand, by the relatively weak
bond of Si-O--Me (Me representing an atom of metal). This applies par-
ticularly in a case involving a bond between this anion and a uni-
valent cation.
Damage to this weaker bond occurs in the presence of water or
diluted ecids on the surface of glass primarily due to the effects of
hydrogen (eventually hydroxonium) ions during formation of a layer of
a gel of silicic acid according to the formula
^OO-Me	 ^O ^ O-H-H+	 2O
Si	 -f- 2 H3O =	 Si	 + 2 Me
^O O-Me' O-H-H2O
During ei. • triating of hydroxides in the course of etching the
thickness of the gel layer in:reases with time, unless there occurs
a mechanical removal- of the layer. The speed with which this layer
is formed is limited by diffusion of water through this gel and it
is only of an approximately parabolic character (Keppeler 1934, Ber-
ger 1936). For this reason it is difficult to extrapolate :he results
of relatively short-term laboratory experimentE to period covering
millions of years.
The described reaction does not occur in the case of silica glass
in which the bond bet%teen silicon and metal is absent (Kaller 1957);
thus silica glass, which is contained in moldavites in the form of
2
•a a
lechatelierite grains and fibers, is more resistant against the ef-
fects of neutral and acid solutions. Under natural conditions the
chemical resistance of lechatelierite is additionally enhanced by
its favorable mechanical properties.
Therefore, a direct proof of surface layer losses could be con-/141
stituted by the length of lechatelierite protrusions on moldavites
which in view of the specified properties became retained after the
occurrence of basic mass etching.
It is hard to assume that lechatelierites, which are found on
the surface of some moldavites and are often of a thickness of only
several thousandths of a mm, could have survived their impact on the
terrestrial surface and, consequently, had to be formed by etching
of the basic substance. On the other hand, it is easy to assume
that the protrusions which were formed by etching could have become
broken off aftc:r reaching a certain length in the sedimental layer,
be it in the course of millions of years or during removal from the
sediment yielding moldavites. In the latter case it can be expected
that lechatelierite fragments will be found in close proximity of
moldavites. To verify this contention we examined some moldavite lay-
ers in the sand deposits southeast of Vrabec which we considered suit-
able for these purposes due to, among other reasons, their age (Bou-
ska 1964). We accumulated a substantial number of lechateliierite
fragments during the 1978 season.
At this occasion we found a moldavite--now inventory number 354
in private collection--(dimensions 25xl7x8 mm, weight 2.25 g) that
could be removed with at least a partially undamaged layer in which
remained imbedded broken-off lechatelierite:. The contributory cir-
cumstance was the fact that the sand and clay layer was permeated by
ferrous compounds that helped to fixate the fragments.
Experimental Part
a) Acquisition of Loose Lechatelierite Fragments
3
Ur^:.
MINE"
aORIGNAL PAGE tS
OF POOR QUALITY
Sand from the immediate vicinity of the found moldavites was e-
lutriated. The finest part of clayey particles was decanted. Larger
particles were removed by mechanical methods and the remaining finer
residue was evaporated. Lechatelierite fragments were removed from
this fraction mechanically under a microscope.
b) Counting and Measuring of Lechatelierite Fragments on the
Surface of Moldavite and Determination of the Overall Length
of Lechatelierite Fibers in Moldavite
Lechatelierite fragments in the individual fields of mol-
,cavite no. 354 were added up under a microscope. Data regarding the
number of fragments in individual fields are shown in Table 1.
TABLE 1.
1 2 3 4 5 e
Polo
Poaet
lecha- Plocha Podet ks
Sumdrai
ddlka Odlep-
tellerltd v mm= no mm= no mm= t4no mm
A 211 28,8 7,9 2,8 4,5
B 28 5,4 • '	 8,7 119 3,1
C 18 2,7 2,4 3,9
D 13 2,9 4,5 1,8 .2,8
E 28 4,3 8, 1 2,2 3,5
Average .i.5
Key to column headings: 1 - Field; 2 - Number of lechtelierites;
3 - Area in sq mm; 4 - number of pieces per sq mm; 5 - Summary
length per cubic mm; 6 - mm etched off.
At the same time was measured the length of individual lechate-
lierite fragments inasfar as tLey were visible in the entire extent.
Determination of the summary length of lechatelierite fibers in the
moldavite mass was carried out by means of Konte.'s method (1969) by
measuring under the microscope in toluene immersion. The length of
lechatelierite fibers measured in moldavite mass under immersion in
toluene and the attainable observations under the microscope were di-
vided by the volume of the observed layer.
4
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1?1
ORICMIgL PAGE P8
Results and Discussion ^f POOR QUALITY
Figure 1 shows a group of lechatelierite fragments separated
from the solid phase of moldcvite rinsing waters. Tt Appears that
the fine-grained layers permeated by clay are richtr in lechatelier-
ite fragments than coarse layers easily permeated by water. This
can be connecter, with dispersion of fragments into a higher volume
by the permeating water.
/142
°
80
70
°
60
50
40	 I	 I
30
20
10
Obr. 1 Nikollk lechal , :ierilovtcb Glomi b. separovantch se sedlmentO v okolf vlta elne.
Zvittenl 1 46
Several lechalellerite fragments separated from the sedlm eels surrounding the m oldevr-
tes. Scale 1 : 46
Obr. 2 7.evislosl telnosti vtskyto lechatellerllovtch 6lomk6, saparov..
etch se sedimento. na jejich d61ee. Slallstickt soabor obsohoval 226 kusi
Occurrence rate dependence of lechateliertle fragments separated from
the sediments according to their length. The statistical set consisted
of 228 fregments
Figure I.
pieces
kUS5
Figure 2 shows the relationship between
the number of isolated lechatelierites and
their length. The relatively high average
length of lechatelierites from this set
(228 pieces--average 0.55 mm) can be due
to the methodology of isolation wherein
a part of very small fragments escapes
attention.
Figure 2.
0.1 0.3 0.5 Q7 0,9 1,1 1,3 1.5 17 1^ 2,1 mm
5
J
;RIGMAL PAGE IS
OF POOR QUALITY
Obr. ]
	
Schbmatick6 znbsornbnl vltavin n
z Vrbbte s vyznatenlm polleek A - E, Pa 	 Figure 3 shows a graphical representationkterbm bylo provedeno seltiol lechetelierlto-
vgch iilomk5
Schematic diagram of moldavlte No 151 wills	 of moldavite no. 354 with delineation of
Indicetlon or fields A — E used for the sum-
mation of lechatelier'te fragments 	 fields (marked A-F.) with its preserved
`I	 original layer.
® (3) D
A	 C	 Figure 3.
E
0 2 4 6 8 10 MM
Column 2 in Table 1 shows the number of lechatelierite fragmerts
in individual fields. This table also sho ,rrs the area of the fields
(column. 3) and the concentration of fragments in these fields in
pieces per sq mm (column 4). From the determined average length of
these fragment_ (0.36 mm) and their number is calculated the overall
length c,f lechatelierite fragments in individual fields in a 1 sq mm
area (column 5).
	 !
From these data arid from the average length of lechatelierite ,/143
fragments per cubic mm (0.62 mm) it is possible to determine the lass
that had to be etched off this moldavite to produce an accumulation
of the corresponding amount of lechatelierite fragments. The thus
computed value ranges between 2.6-4.5 mm (average 3.5 nun) for indi-
vidual areas (column 6).
We regard this value as the lower limit, because it is more pro-
bable that a part of lechatelierite fragments failed to be included,
rather than that there occurred a local accumulation of fragments in
the surveyed spots. In addition, consideration must be given to the
fact that in spite of their chemical resistance lechatelierites them-
selves are subjected tc: the effects of etching and mechanical factors./ 144
Such damage to lechatelierite is borne out by Figure 4 showing a high-
ly magnified fragment with localized corrosion. It is of interest to
note the regularity with .!,Ich this fragment had been etched.
6
L-7
n 1 +4^ 1
	 r^.
C*;IrIF!dI_ pG::EM 13
i	 ^ Q l I ALRY
Obr. 4 Slin g korodovaay lecbatelieritovy ulomek s patrnou praridernocti leptfnt. Zvftienl
1 : 141
Considerably corroded Iccbalelierhe fragment demonstrating apparent regularity of etching
process. Scala 1 :144
Figure 4.
As the length of lechatelierite protrusions on the surface of
moldavites only very exceptionally exceeds 2 rnm, the computed values
indicate that a lz: le part of lechatelierite fibers
	 that had been
bared by etching should be dispersed in the form of fragments through-
	
i
out layers yielding rnoldavites, as has been confirmed by other finds
of lechatelierite fragments in the vicinity of other rnoldavites.
The determined values of the etched off surface layer are some-
what lower than those cited in references (Rost 1967). The differ-
ence could be accounted for by the fact that in our case the thick-
ness of the etched-off layer was determined after imbedding in the
sediment.
7
^i).Jj
REFERENCES
MERGER, E., "Principles of Vulnerability of Glasses to Attack by
Chemicals, I."	 jUl no. 14, pp 351-350, 1936.
SOUSKA, V., "Geology and Stratigraphy of Moldavite Occurrences,"
GeogUM. et Goamochiinr. Acta, no. 28, pp 1921-1930, 1954.
HLAVACOVA, E., "Contribution to the Study of Glass Polishint,:
Candidacy Thesis, School of Chemical Technology and the zecho-
slovak Academy of Sciences, 1964.
JEZEK, B., "The Surface of Moldavites," , priroda, no. 9, p 295, 1911.
CALLER, A., "Polishing of Glass," Jenaer Jahrbuch 1957, p 143.
KELLER, W. O. and HUANG, W. H., "Aqueous Dissolution of Moldavite
and Obsidian at Room Temperature," Acta 'Univorsitatis Caroligie,
Geolocica, pp 309-318, 1971.
KEPPELER, G. and THOMAS-WELZOW, M.,"Detrimental Effects of mater on
Calcium.-Alkali-Silicic Acid Glasses," Keremische Rundschau, no 42,
pp 95, 122, 136, 1934.
KONTA, J. and MRAZ, L., "Chemical Composition and Bulk Density of
Moldavite, 11	 h	 him. Acta no. 33, pp 1103-1111, 1969.
O'KEEPE, J. A., "Tektite Sculpturing," ,
 GeolbiM. et
 Cosmochim. Acta
no 31, p. 1931, 1957.
ROSICKY, V., "Moldavites and Similar Mysterious Glasses," Veda a
i^ vot, no. 5, pp 95-103, 145-154, 1939.
ROST, R., "Behavior of Moldavites in Polarized Light," &C-to Uniyersi-
tatis Carolinpet' Gsoloaica, no. 2, pp 95-112, 1967.
WEYL, W. A., "Some Practical Aspects of the Surface. III, IV.,"
Industry no. 28, pp 349-353, 370, 372, 374, 375-382, 408-412,
428, 430, 432, 1938.
8


Etching of moldavities under natural conditions

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