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Did the moldavites originate from smelted granulite?
Chemical Geology Elsevier Publishing Company, Amsterdam - Printed in The Netherlands
DID T H E M O L D A V I T E S O R I G I N A T E F R O M S M E L T E D G R A N U L I T E ?
V. PATROVSKY Hoiandskd 7, Prague (Czechoslovakia) (Accepted for publication September 19, 1972)
ABSTRACT Patrovsk37, V., 1972. Did the moldavites originate from smelted granulite? Chem. Geol., 10: 249-251. The word"Moldavite" is a special term used for tektites found in a small area of south Bohemia and Moravia. In Bohemia they are found in the strip extending in a southwesterly direction south of the city of ~esk6 Bud~joviceand in Moravia they may be found in the valley of the little river Jihlava. Several hypotheses have been put forward as to the origin Ofmoldavites, but at the present time no reliable explanation is acceptable. INTRODUCTION The properties of moldavites have been known for a long time. They are of a dirty green colour due to bivalent iron, but those from Moravia are of a brown hue caused by some tervalent iron. The chemical composition of both kinds of moldavites is nearly the same; about 78% SiO2, 0.4% TiO2, 11% A12Oa, 2.4% FeO + Fe203, 2.7% CaO, 1.8% MgO and 3.5% K20. It is very interesting that tektites from different world localities have a very similar chemical composition for nearly all components. This fact gave rise~to the hypothesis of a cosmic origin from the same object. In addition Ehman and Kohman (1958) have found the isotopes 1°Be and 26A1in some tektites. The aerodynamic analysis of tektites by Adams and Huffaker (1962) indicates, however, that tektites could not have survived passage through the atmosphere. Another survey denies the isotopic contents and most theories concerning an origin due to lightning, dessication of silica gel, or from volcanoes (lunar or terrestrial) are to be discarded. For example Oswald (1942) suggested the melting of a large aerolithe failing into the earths' atmosphere. IMPACTAND THE RIES CRATER THEORY In recent years Cohen (1961) published the impact hypothesis, based on the possibility of the fall of a meteorite, comet or asteroid. Adler et al. (1962) and Gentner (1961) have suggested that a moldavite-strewn field may have resulted from the same impact which produced the Ries crater in southern Germaay,.Kop_eck,v (1970) oldie_orsto these, the_o.ties, in that the chemical compositions of flue moldaadtes and the suevites found Lri the Rie.~
250
V. PATROVSKY
crater and local rocks are quite different, In addition, the chemical comoosition of suevites varies to a great extent, contrary to that of moldavites and tektites. Also the great distance ( 2 5 0 - 4 1 3 km) between the Ries crater and the Czech moldavite-strewn fields located in only two narrow bands, makes this theory unacceptable. WERE MOLDAVITES FORMED FROM LOCAL VOLCANIC ROCKS? Lovering (1960) pointed out that tektites may be formed from melted granite, but direct comparisons performed by Urey and Mason (1969) were not too favourable due to the high alkali content in granite. Lovering found a loss of about 12% of sodium and 6% potassium oxide after granite melted. The content of SiO2 and FeO remained nearly the same, but MgO, CaO and A1203 were enriched by about 20-40%. The authors' preliminary experiments with granulite lead to the same results. Granulite is a rock similar to granite, but formed mainly from quartz and feldspar. As minor components, garnet, or rarely kyanite, pyroxene or muscovite are present. The most surprising fact is that Bohemian and Moravian moldavites are associated with granulite. There is no known area of granulite in other places. The relationship between moldavites and granulite seems obvious, but the origin of the melting process is still unknown up to the present. All the mentioned theories proved to be inadequate. In Table I some analyses of moldavites, graniteand granulite are summarised. More detailed information about tektites can be found in O'Keefe (1963). TABLE I Comparison of the average chemical composition of moldavites, granite and granulite Composition (%)
SiO2 TiO 2 A120~ Fe203 FeO MnO CaO MgO K20 Na~O
moldavites
granite
~ranulite
melted granulite
78 0.5 11 0.4 2
75 0.4 12 0.5-1.5 1-2
74 0.4 11 0.5 1.~
76 0.5 12 0.5 1.5
0.07 2 1.8 3.5 0.5
0.1 2 1 4.5 3
0.05 2 1 4.5 2.5
0.06 2.5 1.5 4 1.5
REFERENCES Adams, E. and Huffaker, R.M., 1962. Nature, 193: 1249-1255. Adler, I., Chao, E.C.T., Dwotnik, E.J. and Littler, J., 1962. Science, 135: 97.
MOLDA¥ITES FROM SMELTED GRANULITE?
251
Cohen, A,J,, 1961. A semi-quantitative hypothesis of tektite origin by asteroid impact. J. Geophys. Res., 66: 2521. Ehman, W.D. and Kohman, T.P., 1958. Geochim. Cosmochim. Acta, 14: 340-364. Genter, W., Lippolt, H.J. and SchaeffeL A.A., 1961. Z. Naturforschung, 16a: 1240. KopeckS, L., 1970. Note Concerning the Origin of Moon Craters and Astroblemes. National Museum, Prague. Lovering, J.F., 1960.Nature, 186: 1028-1030. O'Keefe, J., 1963. Tektites. Chicago University Press, Chicago, 304 pp. Oswald, J., 1942. Meteoritic Glass. Czech Nature Publishing Co. Urey, H.C. and Mason, B., 1959.Nature, 183: 254, 1119.
DID T H E M O L D A V I T E S O R I G I N A T E F R O M S M E L T E D G R A N U L I T E ?
V. PATROVSKY Hoiandskd 7, Prague (Czechoslovakia) (Accepted for publication September 19, 1972)
ABSTRACT Patrovsk37, V., 1972. Did the moldavites originate from smelted granulite? Chem. Geol., 10: 249-251. The word"Moldavite" is a special term used for tektites found in a small area of south Bohemia and Moravia. In Bohemia they are found in the strip extending in a southwesterly direction south of the city of ~esk6 Bud~joviceand in Moravia they may be found in the valley of the little river Jihlava. Several hypotheses have been put forward as to the origin Ofmoldavites, but at the present time no reliable explanation is acceptable. INTRODUCTION The properties of moldavites have been known for a long time. They are of a dirty green colour due to bivalent iron, but those from Moravia are of a brown hue caused by some tervalent iron. The chemical composition of both kinds of moldavites is nearly the same; about 78% SiO2, 0.4% TiO2, 11% A12Oa, 2.4% FeO + Fe203, 2.7% CaO, 1.8% MgO and 3.5% K20. It is very interesting that tektites from different world localities have a very similar chemical composition for nearly all components. This fact gave rise~to the hypothesis of a cosmic origin from the same object. In addition Ehman and Kohman (1958) have found the isotopes 1°Be and 26A1in some tektites. The aerodynamic analysis of tektites by Adams and Huffaker (1962) indicates, however, that tektites could not have survived passage through the atmosphere. Another survey denies the isotopic contents and most theories concerning an origin due to lightning, dessication of silica gel, or from volcanoes (lunar or terrestrial) are to be discarded. For example Oswald (1942) suggested the melting of a large aerolithe failing into the earths' atmosphere. IMPACTAND THE RIES CRATER THEORY In recent years Cohen (1961) published the impact hypothesis, based on the possibility of the fall of a meteorite, comet or asteroid. Adler et al. (1962) and Gentner (1961) have suggested that a moldavite-strewn field may have resulted from the same impact which produced the Ries crater in southern Germaay,.Kop_eck,v (1970) oldie_orsto these, the_o.ties, in that the chemical compositions of flue moldaadtes and the suevites found Lri the Rie.~
250
V. PATROVSKY
crater and local rocks are quite different, In addition, the chemical comoosition of suevites varies to a great extent, contrary to that of moldavites and tektites. Also the great distance ( 2 5 0 - 4 1 3 km) between the Ries crater and the Czech moldavite-strewn fields located in only two narrow bands, makes this theory unacceptable. WERE MOLDAVITES FORMED FROM LOCAL VOLCANIC ROCKS? Lovering (1960) pointed out that tektites may be formed from melted granite, but direct comparisons performed by Urey and Mason (1969) were not too favourable due to the high alkali content in granite. Lovering found a loss of about 12% of sodium and 6% potassium oxide after granite melted. The content of SiO2 and FeO remained nearly the same, but MgO, CaO and A1203 were enriched by about 20-40%. The authors' preliminary experiments with granulite lead to the same results. Granulite is a rock similar to granite, but formed mainly from quartz and feldspar. As minor components, garnet, or rarely kyanite, pyroxene or muscovite are present. The most surprising fact is that Bohemian and Moravian moldavites are associated with granulite. There is no known area of granulite in other places. The relationship between moldavites and granulite seems obvious, but the origin of the melting process is still unknown up to the present. All the mentioned theories proved to be inadequate. In Table I some analyses of moldavites, graniteand granulite are summarised. More detailed information about tektites can be found in O'Keefe (1963). TABLE I Comparison of the average chemical composition of moldavites, granite and granulite Composition (%)
SiO2 TiO 2 A120~ Fe203 FeO MnO CaO MgO K20 Na~O
moldavites
granite
~ranulite
melted granulite
78 0.5 11 0.4 2
75 0.4 12 0.5-1.5 1-2
74 0.4 11 0.5 1.~
76 0.5 12 0.5 1.5
0.07 2 1.8 3.5 0.5
0.1 2 1 4.5 3
0.05 2 1 4.5 2.5
0.06 2.5 1.5 4 1.5
REFERENCES Adams, E. and Huffaker, R.M., 1962. Nature, 193: 1249-1255. Adler, I., Chao, E.C.T., Dwotnik, E.J. and Littler, J., 1962. Science, 135: 97.
MOLDA¥ITES FROM SMELTED GRANULITE?
251
Cohen, A,J,, 1961. A semi-quantitative hypothesis of tektite origin by asteroid impact. J. Geophys. Res., 66: 2521. Ehman, W.D. and Kohman, T.P., 1958. Geochim. Cosmochim. Acta, 14: 340-364. Genter, W., Lippolt, H.J. and SchaeffeL A.A., 1961. Z. Naturforschung, 16a: 1240. KopeckS, L., 1970. Note Concerning the Origin of Moon Craters and Astroblemes. National Museum, Prague. Lovering, J.F., 1960.Nature, 186: 1028-1030. O'Keefe, J., 1963. Tektites. Chicago University Press, Chicago, 304 pp. Oswald, J., 1942. Meteoritic Glass. Czech Nature Publishing Co. Urey, H.C. and Mason, B., 1959.Nature, 183: 254, 1119.