- Email: [email protected]
Chemical composition and bulk density of moldavites
Geochimica et Cosmochimics Acts, 1969,Vol. 33, pp. 1103to 1111. Pergamon Press.Printedin Northern Ireland
Chemical composition and bulk density of moldavites J. KONTA and L. MRBZ Department of Petrology, Charles University, Prague, Czechoslovakia (Received 30 March 1969; accepted in revisedfomn 18 April 1969) Ab&a&-The weight, dimensions, bulk density, abundance of bubbles, abundance of lechatelierite, size frequency of lechatelierite and maximum projection sphericity were determined in thirty five moldavites (29 from the Bohemian and 6 from Moravian localities). Fifteen new chemical analyses of Bohemian moldavites are reported. Chemical composition and size frequency of lechatelierite, were the factors determining the bulk density of moldavites. The density decreases with increasing SiO, content, and with the decrease of A&O,, Fe*O, + Fe0 (and total Fe,O,), Na,O + K,O and, in particular CaO, and with increase of bubbles. The moldavites of the Bohemian and Moravian localities appear to belong to one event. The results obtained support the theory of the impact source area west of Czechoslovakian tektite localities. INTRODUCTION
purpose of the present paper is to quantitatively determine the factors influencing the bulk density of moldavites as an aid to the elucidation of moldavite genesis. The moldavites are inhomogeneous in many respects. The results also permit deductions about their thermal history and the influence of the source material on the resultant physical and chemical character of moldavites. THE
SAMPLES
Fifteen moldatives were collected and chemically analyzed from four localities in southern Bohemia where they are found in gravel-bearing sands of Upper Miocene to Quaternary age (KONTA, 1966). Of another twenty moldavites that were not chemically analyzed, 14 specimens come from Bohemian localities and 6 from Moravia. Samples of various forms, with different bubble shapes and different amounts of lechatelierite, were selected for study. For each moldavite the sample number locality, colour, weight, number of bubbles, integrated axes of bubbles expressed in mm and, finally, the abundance of bubbles, are deposited with NAPS.* Similar data are also placed in documentation for lechatelierite. BULK DENSITY
Bulk density was determined in carefully cleaned moldavites. The maximum deviation from the average value was fO.001 which represents the maximum error in the determination of bulk density. The densities range from 2.398 to 2.311. These are in accord with the frequency curve of densities as determined by CHAPMAN et cd. (1964) in 108 Bohemian and 37 Moravian moldavites. * For the tables order NAPS Document 00406 from ASIS National Auxiliary Publication Service, c/o CCM Information Sciences, Inc. 22 West 34th Street, New York, New York 10001, remitting $1.00 for microfiche or $3.00 for photocopies. 1103
SHAPE AND
ABUNDANCE
OF
Ru~3ur.w
Six types of bubble shapes, ranging from linear to spherical have been differen tiated. No relationship between the bulk density of moldavites and bubble shape has been found. Frequency of bubbles was measured under the microscope on moldavit,es immersed in benzene at a magnification of 20 x . The total number of bubbles and the sum of axes of bubbles was established in a strip 1 mm in width x 2 mm (de@h of the sharpness of objective) along the breadth and in a space 1 :< 2 mm a,long the length of the tektite. BARNES (1964) introduced the method of relative abundance of bubbles and of lechatelierite in a scale assigning a numerical value t,o the abundance of particles from 0, if lechatelierite or bubbles are absent, to 7 for the specimens containing the most part’icles. ABUNDANCE OF LECHATELIERITE The abundance of lechatelierite was measured under the microscope over the whole observed area of the sample in benzene. An integrated length of the longer axes of grains and broader parts of schlieren (in mm) is divided by a measured area (in cmz). Thus for example in sample 1046 the integrated length of lechatelierite grains is 7.60 mm and the measured area of moldavite is 3.47 cm2; 7.60/ 3.47 = 2.19 which represents the bulk abundance of lechatelierite of one sample. The dependence of bulk density of moldavites on abundance of bubbles and on abundance of lechatelierite is not linear. Although the value of bulk density seems to be influenced by the lechatelierite content, chemical composition and the thermal history of glass will be shown to be the dominant factors. Abundance of bubbles exerts a secondary influence only. Higher contents of lechatelierite cannot increase the bulk density of moldavites as the density of pure lechatelierite is 2.2. The higher bulk density is caused by relatively higher content’s of Fe, K and especially Ca. RELATIONSHIPS BETWEEN THE ABUNDANCE OF LECHATELIERITE, THE ABUNDANCE OF BUBBLES AND THE SPHERICITY OF MOLDAVITES Figure 1 illustrates the relationship between the abundance of lechatelierite This relationship is not linear for and the abundance of bubbles in moldavites. all moldavites but is linear in several groups of moldavites. Tn a,11linear groups the bulk abundance of bubbles decreases with decreasing abundance of lechatelierite. This indicates that there exist several groups with primary differences in lechatelierite contents. Another factor helping to reconstruct the thermal history of tektite glass is the sphericity of moldavites (Table 1). If the maximum projection sphericity is introduced into the relation with the abundance of lechatelierite (Fig. 2), about 80 per cent of the experimental points lie within the same linear series as in Fig. 1. The relationship cannot be identical as numerous moldavites are represented only by fragments whose sphericity could have been different. The maximum projection sphericity observed in samples with bulk abundance of lechatelierite less than 4 increases with a decreasing content of lechatelierite. Where the value exceeds 4 the maximum projection sphericity does not show an increase. This relationship can be interpreted as an influence of different viscosity dependent
Chemical composition and bulk density of moldavites
LECHATELIERITE,
BULK
1105
ABUNDANCE
Fig. 1. Relationship between the abundance of lechatelieriteand the abundance of bubbles in moldavites. l Chemically analyzed samples, 0 Samples not chemically analyzed.
on thermal history during the formation of moldavite shapes. In individual series the cooler and least fluid moldavites occurred in samples with a relatively In samples with bulk abundance of lechatelierite high content of lechatelierite. exceeding 4 the viscosity of glass was considerably higher and the resultant forms of moldavites were flatter or rod-like. The experimental points for Moravian moldavites and for sample 23 from the northern part of a strewn field in Bohemia (Radomilice) are found (Fig. 2) in the region of lowest contents of lechatelierite and of relatively high values of maximum projection sphericity. SIZE FREQUENCY OF LECHATELIERITE GRAINS Frequency curves of the size of lechatelierite are expressed as a number of lechatelierite grains in four size fractions over the area of 10 cm2 (depth about 2 mm). In the majority of moldavites with relatively low density lechatelierite is perceptibly finer and less abundant or is completely dissolved in surrounding glass matrix.
_--___
No. of moldavitc and locality --_-. -_ .
24 397 1040 1046 1052 1095 1125 1140 801 816 250 682 885 1266 23
Lo&mice Lo&mice Lo&mice LoEenice Lodenico Lodenice Lodenice L&&co Bukoveo Bukoveo Lhenice Lhenioe Lhenice Lhanice Rltdomilice
27 28 30 1037 72 75 77 84 88 800 189 235 237 882
Besednioe Besednice Besednice LoEeniee Nesmeii Nevmeii Nesmeii N&hov NBcbov Bukovec Vrdbde V&b& VrQbEe Lhenioe
624 626 626 627 629 1542
Dukovany Slevlttice Slav&ice Slav&ice Step&novice Suohohrdly
39.Q 39.1 41.0 Z&2 24.4 29.7 28.5 32.5 24.9 23*5 31.0 21.3 26.3 34.3 37.0 Bob~mb 31-t 35.0 26.2 48*S 31.3 30.2 26.9 30.7 52.9 18.7 34.0 29.1 29.8 22.6 ?&xwia 50.8 44*0 24*5 26.8 25.7 28.1
14-6 15-4 26.9 17.2 19.7 12.3 26.9 27.0 16.8 20.6 20.4 11.8
IO.4 6.1 4.9 11.1 9.3 5.0 10.0 14-5 3-8 16.3 ti.0 4.4
0.26 0.13 0.12 0.46 0*3K 0.17 0.38 0.49 0.16 O*GQ O*fQ n.21
18.7 23.7
11.9 14.3
(I.35 0.39
17.0
5.1
(ercmples not chemicltlly 13.1 24.9 16.5 10.7 18.1 13.8 l4.l 20-2 14.3 12.0 20.8 18.2 15.4 12,l
5.5 12.1 5.1 6.5 12-7 7.6 7.7 7.7 II-5 3.1 3.9 10.0 8.5 3.7
(samples not ohemically 35.8 18.2 21.0 22.6 21.9 lQ.9
14.4 14.8 21.0 19.6 18.3 17.1
0.1Y
0.39 0.53 0931 0.70 0.09 0.31 0.38 0.40 0.42 0.66 0.44 0.70 0.69
0.58 0.35 0.28 0.67 0.57 0.40 0.50 0.63 0.32 0-82 0.39 0.43 0.39 0.60 0.62
O.Sl o-44 0.46 0.88 0.71 0.72 0.67 0.46 0.93 0.43 0.44 0.57 0.68 0.56
0.42 0.58 0.38 0.39 0.66 0.52 0.54 0.46 0.57 0.35 0.26 0.57 0.54 0.37
0.41 0.88 1.00 0.58 0.51 0.75
0.48 0.66 0.95 0.86 0.84 0.81
0.8fl 0.70
ftnaiyzod) 0.18 0.36 0.19 Cl.11 0.41 0.25 0.29 0.25 0.22 0.17 0.11 0.34 0.29 0.16 canrslyzed) 0.28 0.34 0.80 0.73 0.71 O-61
The moldavites from linear series with the highest ratio of bulk abundance of bubbles to abundance of lechatelierite (upper series starting with Nos. 801,75 and 1040 in Fig. I.) reveal the finest size frequency of lechatelierite. As some of these samples (Nos. 800, 682) contain also markedly angular lechatelierite grains, it is most probable that the moldavites with abundance of lechatelie~te below the -value 4 originated from the relatively finer source material. The moldavites formed from relatively finer source material contained a higher amount of volatilea and produced alaxger amount of bubbles in comparison with the content of lechatelierite. A silty-sandy clay would be the equivalent of this material on Earth.
Chemical composition and bulk density of moldavites
1107
1. Fig. 2. Relationship
between the abundance of leohatelierite and the sphericity of moldevites.
RELATIONBETWEENCHEMICALCOMPOSITION AND DENSITY OF MOLDAVITES Table 2 reports chemical analyses of 15 moldevites from four Bohemian localities. Fe0 was not determined in two samples and MnO in five samples because of insufficient material. Figure 3 shows the values of bulk density in relation to major oxides. Density decreases roughly with increasing SiO, content. The moldavites with the lowest SiO, content show the relatively highest contents of lechatelierite with grains which are often still angular. The content of lechatelierite decreases stepwise with an increasing SiO, content. The contents of other oxides show a slight decrease with decreasing bulk density. A distinct decrease of bulk density with an increasing SiO, content is the result of the dissolution of lechatelierite grains in surrounding glass and of the lowering of content of other oxides in glass matrix. From the graph (Fig. 3) it can be seen that the oxides in moldavites are divided into two groups. The oxides of the first group (SiO,, MgO and especially CaO) reveal sympathetic variations in almost the whole course of the graph. The
,J. KOETA
1108 Table
2. Chemical analyses of moldavites, (Analyst.: Dr. T,. M&z)
Nos. 24 _______.__._~~~
397
1040 ~~~~._~_. ~_~
SiO, TiO, Al,O, %O, Fe0 MnO MgO CaO NC%,0 GO
x1.27 0.31 9.46 0.61 1.28 0.02 1.52 1.62 0.48 3.27
80.72
Total Total Fe,O,
99.84 2.03
99.71 I.$!4
0.28 9.12 II.51 I.15 1l.d. 1.97 2.58 0.39 2.99
78~36 0.36 IO.20 1.22 1.83 0.02 1.86 1.96 0.62 3.28 99.71 3 2Ti
Bukovea NOS.
and L.MRAz Bohemia
IO.46 .._~~
1052
80.29
75.5 9
0.29 9.59 0.41 1.19 om I.96 2.56 0.45 3.01 _-. 99.78 1.73
0.36 IO.46 n.70 I.68 0.03 2.35 3.96 (I.66 3.81
10!1.2 YX.i:!
0.,X$ IO.22 Il.Cl. 11.11. 2.14 2.37 0.45 3.27
zal 2.5i
-G50 2.26 .~ 99.76
Ihnicr
..___
1125
1110
;cJ.p a
71.5i 0.35 9.91 0.43
Il.33 8.8” WO2 1 fit) 0.07 2.43 2.98 0.49 3.65
1.80
0.05 2.48 2.77 0.62 3.78
QY.76 ‘I.36
Radomiline __-
801
Xl6
250
SiO,
79.27
78.71
79.07
78.94
78.46
59.39
85.09
Al,& TiO Fe,O, Fe0 MI10 MgO Cm0 Na,O GO
9.63 0.31
0.30 Q.74 0.43 I.48 0.03 2.03 3.00 0.50 3.45
0.27 9,48 0.54 1.33 0.03 2.10 3.11 0.50 3.55
10.49 0.32 1.28 1.41 md. 1.39 2.01 0.53 3.44
0.27 9.83 0.48 1.18 1l.d. 2.64 3.54 0.44 3.28
IO.23 0.36 il.93 1.66 0.02 1.34 1.62 0.67 3.60
0.24 7.32 0.50 0.79 0.03 1.48 1.81 0.26 2.46
99.67 2.07
99.98 2.02
99.81 2.85
100.12 1.79
--99.82 2.77
99.97 1.38
Total Total Fe,O,
1l.d. I1.d. 1.97 2.62 0.48 3.54 97.82 1.99
682 --__-.__
885
1256 -..---____
23
99.81 n.d. =
not determined due to small amount of sample.
oxides of the second group (FeO, total Fe,O,, K,O or Na,O + K,O, and A&O,) show inverse relations. Samples Nos. 1256, 682 and 1040 display the highest contents of fine lechatelierite from the chemically analyzed samples plotted in Fig. 3. These moldavites record the largest decrease of SiO, and CaO and a substantial reduction of CaO The bulk abundance of bubbles in accounts for the decrease of bulk density. these moldavites is very low and the tektite glass more fluid and the forms The moldavites with relatively abundant fine-grained lechamore spherical. telierite originated by the melting of source material containing relatively finer quartz and a higher content of other fine mineral particles whose major components were SiO,, Al,O,, Fe203, FeO, K,O( +Na,O). The minerals containing calcium and magnesium were less abundant in these finer source materials while in the source material with originally coarser quartz their contents were higher (Nos. 1052, 885, 250, 816, 1125, 397). PHILPOTTS and PINSON (1966) have found that the Moravian moldavites have lower and relatively constant average contents of MgO and CaO, whereas Bohemian tektites have high and variable alkaline earth contents. They
Chemical composition and bulk density of moldavites
1109
85
L_I.__L__
2.400
2.380
L-I.
_1__1_..l__-_Lo
2.360
BULK
2.340
2.320
DENSITY
Fig. 3. Density in relation to major oxides of moldavites.
explained the variations in chemical composition within and between individual moldavites in terms of fractional volatilization that occurred during the brief thermal event. According to TAYLOR (1966) the evidence from the impact-glassparential sediment relationships at Henbury suggests that the differences in composition are primary, and not caused by the melting process. The chemical composition, the size frequency of lechatelierite and the size frequency of mineral constituents of the source material are the decisive factors the thermal history is an important controlling the bulk density of moldavites; additional factor. The Moravian moldavites and some samples from the northernmost part of Bohemian localities contain lesser amounts of lechatelierite, lesser amounts of small bubbles, and their bulk density is lower than that of moldavites from other Bohemian localities. The Moravian moldavites along with the samples from the northern localities of the strewn field in Bohemia reveal on the average the largest sphericity (KONTA, unpublished data). Assuming that more fluid tektite glass must have experienced a higher temperature it can be concluded that the hotter
part of the moldavite strewn field is in Moravia and in the northernmost, part of t 1111 strewn field in Bohemia. If we accept t,he impact, t,heory of moldavit,c: origin tJllrill the greatest mechanical energy has been effective where the highest thermal energy was released. Consequently, the less heated moldavitex with high bulk abundance of lechatelierite and bubbles, with less fluid glass and with tlatter CLI’ rod-like forms, were transport,ed from Ohe site of impact] by a relatively ~w\-w amount. of energy over smeller distances, they travelled 011 a shorter and IOU, trajectory. Moldavites in which lechatelierite completely dissolved in glass matrix, with fewest bubbles, that were more fluid and hence more spherical, WXY ejected with greater energy and transported mostly over larger distances from t,he site of impact, or if they occur not far from the impact, they were ejected on steep and high trajectories. These facts are consistent with the origin of moldavites from the Ries crater. CONCLTJSIONS 1. The ratio of abundance of lechatelierite to the abundance of bubbles is not linear for all moldavites but it is linear in several moldavite groups. This ratio is assumed to depend both on original source material and on thermal history. 2. The maximum projection sphericity of moldavites in linear series with abundance of lechatelierite less than 4, increases with decreasing content of lechatelierite. 3. Moldavites with the highest values of ratio of abundance of bubbles to abundance of lechatelierite display, on the average, the finest size frequency of lechatelierite and therefore it is postulated that they originated from the most fine grained source material. 4. The major oxides in moldavites can be divided into two groups. In the first group the SiO,, (MgO + CaO) and especially CaO show sympathetic variations in dependence on bulk density (Fig. 3). Inverse variations were recorded in Al,O,, Fe,O, and Fe0 (and total Fe,O,) and in the sum (Na,O + K,O). The deviations from linear increase of SiO, with gradually decreasing density were caused by variations in grain size and composition of source material. 5. Relatively less heated moldavites were ejected from the site of impact by a relatively smaller amount of energy over shorter distances; they flew on a shorter The glass of these moldavites was less fluid at the time of and low trajectory. their origin with resulting flatter or rodlike forms and with a higher bulk density. The hotter moldavites were ejected by relatively higher energy over greater distances from the site of impact, or in some cases in shorter distances but with steep and high trajectories. Their lechatelierite was more completely melted and they became relatively richer in silica; the abundance of bubbles in these moldavites is very low and the more heated tektite glass was more fluid and the forms of these moldavites more spherical. In spite of their lower density these moldavites are The moldavites of the Bohemian assumed to have been larger on the average. and Moravian localities belong to one event. These results together with similar K-A ages (14.5 to 15.1 m.y.) for Bohemian and Moravian moldavites (ZXHRINGER, 1963) and the similar age of 14.8 & 0.7 m.y. for the glass separated from suevite
Chemical composition and bulk density of moldavites
1111
from the region of the Ries Kessel (GENTNER et al., 1963) suggest that the Ries crater, Bavaria, would be the source of moldavites. REFERENCES BARNES V. E. (1964) Variation of petrographic and chemical characteristics of indochinite tektites within their strewn-field. Geochim. Cosnzochinz.Acta 28, 893-913. BARNES V. E. (1968) Tektites. Reprinted from I&em&o%& Dictionary of Geophysics, pp. 1-12 Pergamon. CHAPMAN D. R., LARSON H. K. and SCHEIBER L. C. (1964) Population polygons of tektite specific gravity for various localities in Australia. Geochim. Cosmochim. Acta 23, 821-839. GENTNER W., LIPPOLT H. J. and SCHAEBFER0. A. (1963) Argonbestimmungen an Kaliummineralien-XI. Die Kalium-Argon-Alter der Gliiser des Nijrdlinger Rieses und der bohmiscbmtirischen Tektite. Geochim. Cosmochim. Acta 27, 191-200. KONTA J. (1966) Tektites in Bohemia/Central Europe/and their relation to the tektite-bearing sediments. Acta Univ. Carolinae, Geologica No. 2, 81-97. PHILPOTTS J. A. and PINSON W. H. (1966) New data on the chemical composition and origin of moldavites. Geochim. Cosmochim. Acta 30, 253-266. TAYLOR S. R. (1966) Australites, Henbury impact glass and subgreywacke: a comparison of the abundances of 51 elements. Geochim. Cosmochim. Acta 30, 1121-1136. Z&RINGER J. (1963) Isotopes in tektites. In Tektites, (editor J. O’Keefe) pp. 137-149. University of Chicago Press.
Chemical composition and bulk density of moldavites J. KONTA and L. MRBZ Department of Petrology, Charles University, Prague, Czechoslovakia (Received 30 March 1969; accepted in revisedfomn 18 April 1969) Ab&a&-The weight, dimensions, bulk density, abundance of bubbles, abundance of lechatelierite, size frequency of lechatelierite and maximum projection sphericity were determined in thirty five moldavites (29 from the Bohemian and 6 from Moravian localities). Fifteen new chemical analyses of Bohemian moldavites are reported. Chemical composition and size frequency of lechatelierite, were the factors determining the bulk density of moldavites. The density decreases with increasing SiO, content, and with the decrease of A&O,, Fe*O, + Fe0 (and total Fe,O,), Na,O + K,O and, in particular CaO, and with increase of bubbles. The moldavites of the Bohemian and Moravian localities appear to belong to one event. The results obtained support the theory of the impact source area west of Czechoslovakian tektite localities. INTRODUCTION
purpose of the present paper is to quantitatively determine the factors influencing the bulk density of moldavites as an aid to the elucidation of moldavite genesis. The moldavites are inhomogeneous in many respects. The results also permit deductions about their thermal history and the influence of the source material on the resultant physical and chemical character of moldavites. THE
SAMPLES
Fifteen moldatives were collected and chemically analyzed from four localities in southern Bohemia where they are found in gravel-bearing sands of Upper Miocene to Quaternary age (KONTA, 1966). Of another twenty moldavites that were not chemically analyzed, 14 specimens come from Bohemian localities and 6 from Moravia. Samples of various forms, with different bubble shapes and different amounts of lechatelierite, were selected for study. For each moldavite the sample number locality, colour, weight, number of bubbles, integrated axes of bubbles expressed in mm and, finally, the abundance of bubbles, are deposited with NAPS.* Similar data are also placed in documentation for lechatelierite. BULK DENSITY
Bulk density was determined in carefully cleaned moldavites. The maximum deviation from the average value was fO.001 which represents the maximum error in the determination of bulk density. The densities range from 2.398 to 2.311. These are in accord with the frequency curve of densities as determined by CHAPMAN et cd. (1964) in 108 Bohemian and 37 Moravian moldavites. * For the tables order NAPS Document 00406 from ASIS National Auxiliary Publication Service, c/o CCM Information Sciences, Inc. 22 West 34th Street, New York, New York 10001, remitting $1.00 for microfiche or $3.00 for photocopies. 1103
SHAPE AND
ABUNDANCE
OF
Ru~3ur.w
Six types of bubble shapes, ranging from linear to spherical have been differen tiated. No relationship between the bulk density of moldavites and bubble shape has been found. Frequency of bubbles was measured under the microscope on moldavit,es immersed in benzene at a magnification of 20 x . The total number of bubbles and the sum of axes of bubbles was established in a strip 1 mm in width x 2 mm (de@h of the sharpness of objective) along the breadth and in a space 1 :< 2 mm a,long the length of the tektite. BARNES (1964) introduced the method of relative abundance of bubbles and of lechatelierite in a scale assigning a numerical value t,o the abundance of particles from 0, if lechatelierite or bubbles are absent, to 7 for the specimens containing the most part’icles. ABUNDANCE OF LECHATELIERITE The abundance of lechatelierite was measured under the microscope over the whole observed area of the sample in benzene. An integrated length of the longer axes of grains and broader parts of schlieren (in mm) is divided by a measured area (in cmz). Thus for example in sample 1046 the integrated length of lechatelierite grains is 7.60 mm and the measured area of moldavite is 3.47 cm2; 7.60/ 3.47 = 2.19 which represents the bulk abundance of lechatelierite of one sample. The dependence of bulk density of moldavites on abundance of bubbles and on abundance of lechatelierite is not linear. Although the value of bulk density seems to be influenced by the lechatelierite content, chemical composition and the thermal history of glass will be shown to be the dominant factors. Abundance of bubbles exerts a secondary influence only. Higher contents of lechatelierite cannot increase the bulk density of moldavites as the density of pure lechatelierite is 2.2. The higher bulk density is caused by relatively higher content’s of Fe, K and especially Ca. RELATIONSHIPS BETWEEN THE ABUNDANCE OF LECHATELIERITE, THE ABUNDANCE OF BUBBLES AND THE SPHERICITY OF MOLDAVITES Figure 1 illustrates the relationship between the abundance of lechatelierite This relationship is not linear for and the abundance of bubbles in moldavites. all moldavites but is linear in several groups of moldavites. Tn a,11linear groups the bulk abundance of bubbles decreases with decreasing abundance of lechatelierite. This indicates that there exist several groups with primary differences in lechatelierite contents. Another factor helping to reconstruct the thermal history of tektite glass is the sphericity of moldavites (Table 1). If the maximum projection sphericity is introduced into the relation with the abundance of lechatelierite (Fig. 2), about 80 per cent of the experimental points lie within the same linear series as in Fig. 1. The relationship cannot be identical as numerous moldavites are represented only by fragments whose sphericity could have been different. The maximum projection sphericity observed in samples with bulk abundance of lechatelierite less than 4 increases with a decreasing content of lechatelierite. Where the value exceeds 4 the maximum projection sphericity does not show an increase. This relationship can be interpreted as an influence of different viscosity dependent
Chemical composition and bulk density of moldavites
LECHATELIERITE,
BULK
1105
ABUNDANCE
Fig. 1. Relationship between the abundance of lechatelieriteand the abundance of bubbles in moldavites. l Chemically analyzed samples, 0 Samples not chemically analyzed.
on thermal history during the formation of moldavite shapes. In individual series the cooler and least fluid moldavites occurred in samples with a relatively In samples with bulk abundance of lechatelierite high content of lechatelierite. exceeding 4 the viscosity of glass was considerably higher and the resultant forms of moldavites were flatter or rod-like. The experimental points for Moravian moldavites and for sample 23 from the northern part of a strewn field in Bohemia (Radomilice) are found (Fig. 2) in the region of lowest contents of lechatelierite and of relatively high values of maximum projection sphericity. SIZE FREQUENCY OF LECHATELIERITE GRAINS Frequency curves of the size of lechatelierite are expressed as a number of lechatelierite grains in four size fractions over the area of 10 cm2 (depth about 2 mm). In the majority of moldavites with relatively low density lechatelierite is perceptibly finer and less abundant or is completely dissolved in surrounding glass matrix.
_--___
No. of moldavitc and locality --_-. -_ .
24 397 1040 1046 1052 1095 1125 1140 801 816 250 682 885 1266 23
Lo&mice Lo&mice Lo&mice LoEenice Lodenico Lodenice Lodenice L&&co Bukoveo Bukoveo Lhenice Lhenioe Lhenice Lhanice Rltdomilice
27 28 30 1037 72 75 77 84 88 800 189 235 237 882
Besednioe Besednice Besednice LoEeniee Nesmeii Nevmeii Nesmeii N&hov NBcbov Bukovec Vrdbde V&b& VrQbEe Lhenioe
624 626 626 627 629 1542
Dukovany Slevlttice Slav&ice Slav&ice Step&novice Suohohrdly
39.Q 39.1 41.0 Z&2 24.4 29.7 28.5 32.5 24.9 23*5 31.0 21.3 26.3 34.3 37.0 Bob~mb 31-t 35.0 26.2 48*S 31.3 30.2 26.9 30.7 52.9 18.7 34.0 29.1 29.8 22.6 ?&xwia 50.8 44*0 24*5 26.8 25.7 28.1
14-6 15-4 26.9 17.2 19.7 12.3 26.9 27.0 16.8 20.6 20.4 11.8
IO.4 6.1 4.9 11.1 9.3 5.0 10.0 14-5 3-8 16.3 ti.0 4.4
0.26 0.13 0.12 0.46 0*3K 0.17 0.38 0.49 0.16 O*GQ O*fQ n.21
18.7 23.7
11.9 14.3
(I.35 0.39
17.0
5.1
(ercmples not chemicltlly 13.1 24.9 16.5 10.7 18.1 13.8 l4.l 20-2 14.3 12.0 20.8 18.2 15.4 12,l
5.5 12.1 5.1 6.5 12-7 7.6 7.7 7.7 II-5 3.1 3.9 10.0 8.5 3.7
(samples not ohemically 35.8 18.2 21.0 22.6 21.9 lQ.9
14.4 14.8 21.0 19.6 18.3 17.1
0.1Y
0.39 0.53 0931 0.70 0.09 0.31 0.38 0.40 0.42 0.66 0.44 0.70 0.69
0.58 0.35 0.28 0.67 0.57 0.40 0.50 0.63 0.32 0-82 0.39 0.43 0.39 0.60 0.62
O.Sl o-44 0.46 0.88 0.71 0.72 0.67 0.46 0.93 0.43 0.44 0.57 0.68 0.56
0.42 0.58 0.38 0.39 0.66 0.52 0.54 0.46 0.57 0.35 0.26 0.57 0.54 0.37
0.41 0.88 1.00 0.58 0.51 0.75
0.48 0.66 0.95 0.86 0.84 0.81
0.8fl 0.70
ftnaiyzod) 0.18 0.36 0.19 Cl.11 0.41 0.25 0.29 0.25 0.22 0.17 0.11 0.34 0.29 0.16 canrslyzed) 0.28 0.34 0.80 0.73 0.71 O-61
The moldavites from linear series with the highest ratio of bulk abundance of bubbles to abundance of lechatelierite (upper series starting with Nos. 801,75 and 1040 in Fig. I.) reveal the finest size frequency of lechatelierite. As some of these samples (Nos. 800, 682) contain also markedly angular lechatelierite grains, it is most probable that the moldavites with abundance of lechatelie~te below the -value 4 originated from the relatively finer source material. The moldavites formed from relatively finer source material contained a higher amount of volatilea and produced alaxger amount of bubbles in comparison with the content of lechatelierite. A silty-sandy clay would be the equivalent of this material on Earth.
Chemical composition and bulk density of moldavites
1107
1. Fig. 2. Relationship
between the abundance of leohatelierite and the sphericity of moldevites.
RELATIONBETWEENCHEMICALCOMPOSITION AND DENSITY OF MOLDAVITES Table 2 reports chemical analyses of 15 moldevites from four Bohemian localities. Fe0 was not determined in two samples and MnO in five samples because of insufficient material. Figure 3 shows the values of bulk density in relation to major oxides. Density decreases roughly with increasing SiO, content. The moldavites with the lowest SiO, content show the relatively highest contents of lechatelierite with grains which are often still angular. The content of lechatelierite decreases stepwise with an increasing SiO, content. The contents of other oxides show a slight decrease with decreasing bulk density. A distinct decrease of bulk density with an increasing SiO, content is the result of the dissolution of lechatelierite grains in surrounding glass and of the lowering of content of other oxides in glass matrix. From the graph (Fig. 3) it can be seen that the oxides in moldavites are divided into two groups. The oxides of the first group (SiO,, MgO and especially CaO) reveal sympathetic variations in almost the whole course of the graph. The
,J. KOETA
1108 Table
2. Chemical analyses of moldavites, (Analyst.: Dr. T,. M&z)
Nos. 24 _______.__._~~~
397
1040 ~~~~._~_. ~_~
SiO, TiO, Al,O, %O, Fe0 MnO MgO CaO NC%,0 GO
x1.27 0.31 9.46 0.61 1.28 0.02 1.52 1.62 0.48 3.27
80.72
Total Total Fe,O,
99.84 2.03
99.71 I.$!4
0.28 9.12 II.51 I.15 1l.d. 1.97 2.58 0.39 2.99
78~36 0.36 IO.20 1.22 1.83 0.02 1.86 1.96 0.62 3.28 99.71 3 2Ti
Bukovea NOS.
and L.MRAz Bohemia
IO.46 .._~~
1052
80.29
75.5 9
0.29 9.59 0.41 1.19 om I.96 2.56 0.45 3.01 _-. 99.78 1.73
0.36 IO.46 n.70 I.68 0.03 2.35 3.96 (I.66 3.81
10!1.2 YX.i:!
0.,X$ IO.22 Il.Cl. 11.11. 2.14 2.37 0.45 3.27
zal 2.5i
-G50 2.26 .~ 99.76
Ihnicr
..___
1125
1110
;cJ.p a
71.5i 0.35 9.91 0.43
Il.33 8.8” WO2 1 fit) 0.07 2.43 2.98 0.49 3.65
1.80
0.05 2.48 2.77 0.62 3.78
QY.76 ‘I.36
Radomiline __-
801
Xl6
250
SiO,
79.27
78.71
79.07
78.94
78.46
59.39
85.09
Al,& TiO Fe,O, Fe0 MI10 MgO Cm0 Na,O GO
9.63 0.31
0.30 Q.74 0.43 I.48 0.03 2.03 3.00 0.50 3.45
0.27 9,48 0.54 1.33 0.03 2.10 3.11 0.50 3.55
10.49 0.32 1.28 1.41 md. 1.39 2.01 0.53 3.44
0.27 9.83 0.48 1.18 1l.d. 2.64 3.54 0.44 3.28
IO.23 0.36 il.93 1.66 0.02 1.34 1.62 0.67 3.60
0.24 7.32 0.50 0.79 0.03 1.48 1.81 0.26 2.46
99.67 2.07
99.98 2.02
99.81 2.85
100.12 1.79
--99.82 2.77
99.97 1.38
Total Total Fe,O,
1l.d. I1.d. 1.97 2.62 0.48 3.54 97.82 1.99
682 --__-.__
885
1256 -..---____
23
99.81 n.d. =
not determined due to small amount of sample.
oxides of the second group (FeO, total Fe,O,, K,O or Na,O + K,O, and A&O,) show inverse relations. Samples Nos. 1256, 682 and 1040 display the highest contents of fine lechatelierite from the chemically analyzed samples plotted in Fig. 3. These moldavites record the largest decrease of SiO, and CaO and a substantial reduction of CaO The bulk abundance of bubbles in accounts for the decrease of bulk density. these moldavites is very low and the tektite glass more fluid and the forms The moldavites with relatively abundant fine-grained lechamore spherical. telierite originated by the melting of source material containing relatively finer quartz and a higher content of other fine mineral particles whose major components were SiO,, Al,O,, Fe203, FeO, K,O( +Na,O). The minerals containing calcium and magnesium were less abundant in these finer source materials while in the source material with originally coarser quartz their contents were higher (Nos. 1052, 885, 250, 816, 1125, 397). PHILPOTTS and PINSON (1966) have found that the Moravian moldavites have lower and relatively constant average contents of MgO and CaO, whereas Bohemian tektites have high and variable alkaline earth contents. They
Chemical composition and bulk density of moldavites
1109
85
L_I.__L__
2.400
2.380
L-I.
_1__1_..l__-_Lo
2.360
BULK
2.340
2.320
DENSITY
Fig. 3. Density in relation to major oxides of moldavites.
explained the variations in chemical composition within and between individual moldavites in terms of fractional volatilization that occurred during the brief thermal event. According to TAYLOR (1966) the evidence from the impact-glassparential sediment relationships at Henbury suggests that the differences in composition are primary, and not caused by the melting process. The chemical composition, the size frequency of lechatelierite and the size frequency of mineral constituents of the source material are the decisive factors the thermal history is an important controlling the bulk density of moldavites; additional factor. The Moravian moldavites and some samples from the northernmost part of Bohemian localities contain lesser amounts of lechatelierite, lesser amounts of small bubbles, and their bulk density is lower than that of moldavites from other Bohemian localities. The Moravian moldavites along with the samples from the northern localities of the strewn field in Bohemia reveal on the average the largest sphericity (KONTA, unpublished data). Assuming that more fluid tektite glass must have experienced a higher temperature it can be concluded that the hotter
part of the moldavite strewn field is in Moravia and in the northernmost, part of t 1111 strewn field in Bohemia. If we accept t,he impact, t,heory of moldavit,c: origin tJllrill the greatest mechanical energy has been effective where the highest thermal energy was released. Consequently, the less heated moldavitex with high bulk abundance of lechatelierite and bubbles, with less fluid glass and with tlatter CLI’ rod-like forms, were transport,ed from Ohe site of impact] by a relatively ~w\-w amount. of energy over smeller distances, they travelled 011 a shorter and IOU, trajectory. Moldavites in which lechatelierite completely dissolved in glass matrix, with fewest bubbles, that were more fluid and hence more spherical, WXY ejected with greater energy and transported mostly over larger distances from t,he site of impact, or if they occur not far from the impact, they were ejected on steep and high trajectories. These facts are consistent with the origin of moldavites from the Ries crater. CONCLTJSIONS 1. The ratio of abundance of lechatelierite to the abundance of bubbles is not linear for all moldavites but it is linear in several moldavite groups. This ratio is assumed to depend both on original source material and on thermal history. 2. The maximum projection sphericity of moldavites in linear series with abundance of lechatelierite less than 4, increases with decreasing content of lechatelierite. 3. Moldavites with the highest values of ratio of abundance of bubbles to abundance of lechatelierite display, on the average, the finest size frequency of lechatelierite and therefore it is postulated that they originated from the most fine grained source material. 4. The major oxides in moldavites can be divided into two groups. In the first group the SiO,, (MgO + CaO) and especially CaO show sympathetic variations in dependence on bulk density (Fig. 3). Inverse variations were recorded in Al,O,, Fe,O, and Fe0 (and total Fe,O,) and in the sum (Na,O + K,O). The deviations from linear increase of SiO, with gradually decreasing density were caused by variations in grain size and composition of source material. 5. Relatively less heated moldavites were ejected from the site of impact by a relatively smaller amount of energy over shorter distances; they flew on a shorter The glass of these moldavites was less fluid at the time of and low trajectory. their origin with resulting flatter or rodlike forms and with a higher bulk density. The hotter moldavites were ejected by relatively higher energy over greater distances from the site of impact, or in some cases in shorter distances but with steep and high trajectories. Their lechatelierite was more completely melted and they became relatively richer in silica; the abundance of bubbles in these moldavites is very low and the more heated tektite glass was more fluid and the forms of these moldavites more spherical. In spite of their lower density these moldavites are The moldavites of the Bohemian assumed to have been larger on the average. and Moravian localities belong to one event. These results together with similar K-A ages (14.5 to 15.1 m.y.) for Bohemian and Moravian moldavites (ZXHRINGER, 1963) and the similar age of 14.8 & 0.7 m.y. for the glass separated from suevite
Chemical composition and bulk density of moldavites
1111
from the region of the Ries Kessel (GENTNER et al., 1963) suggest that the Ries crater, Bavaria, would be the source of moldavites. REFERENCES BARNES V. E. (1964) Variation of petrographic and chemical characteristics of indochinite tektites within their strewn-field. Geochim. Cosnzochinz.Acta 28, 893-913. BARNES V. E. (1968) Tektites. Reprinted from I&em&o%& Dictionary of Geophysics, pp. 1-12 Pergamon. CHAPMAN D. R., LARSON H. K. and SCHEIBER L. C. (1964) Population polygons of tektite specific gravity for various localities in Australia. Geochim. Cosmochim. Acta 23, 821-839. GENTNER W., LIPPOLT H. J. and SCHAEBFER0. A. (1963) Argonbestimmungen an Kaliummineralien-XI. Die Kalium-Argon-Alter der Gliiser des Nijrdlinger Rieses und der bohmiscbmtirischen Tektite. Geochim. Cosmochim. Acta 27, 191-200. KONTA J. (1966) Tektites in Bohemia/Central Europe/and their relation to the tektite-bearing sediments. Acta Univ. Carolinae, Geologica No. 2, 81-97. PHILPOTTS J. A. and PINSON W. H. (1966) New data on the chemical composition and origin of moldavites. Geochim. Cosmochim. Acta 30, 253-266. TAYLOR S. R. (1966) Australites, Henbury impact glass and subgreywacke: a comparison of the abundances of 51 elements. Geochim. Cosmochim. Acta 30, 1121-1136. Z&RINGER J. (1963) Isotopes in tektites. In Tektites, (editor J. O’Keefe) pp. 137-149. University of Chicago Press.