My location: United States

MOLDAVITE DEPOSITS – PAST AND THE PRESENT

 Written by Alexandr Martaus

INTRODUCTION

This short article offers short description and classification of the moldavite deposits located only in the area of the Czech Republic.

The first records about green stones were found near Vltava river comes from the work of professor Josef Mayer (1788) and were marked as chrysotiles. New discoveries of similar matters in the Africa and Australia had shown neighbouring connection to the impact structures similar to the moldavites. The origin of name (Moldavites) is word Moldau, which is Latin name of the Czech river Vltava.

The moldavites originated almost 15 million years ago, when a great meteorites hit the earth surface. Due to the extremely high temperature and pressure of the explosion, the meteorite and the surrounding rocks melted and sprayed some of the glassy substance (moldavite) into region of the Czech Republic, Austria and Germany. The total amount of this glass was estimated to 3 000 tons. Moldavites are noted for many distinquished features. From all, it is the gorgeous green colour, which together with its clarity and originate sculpture of the surface is a predetermination of this precious stone for jewellery.

For the Moldavites belonging to the tektite family [1] are characteristic the unique sculpture and green colour. The tektites from other impact structures as Indochinites, Philippinites or Australites posses’ brown or black colour, and the surface is smoothed or weakly corroded.

As all tektites from other localities in the world moldavites possess a fluid-like structure and they contain small particles of the lechatelierite and bubbles of gas. Green natural glasses occur in the small areas in the Czech Republic and Germany from the North or Northeast of Ries meteorite crater in Germany.

Occurrences of moldavites are located in three mainly detached places – South Bohemia, Western Moravia and western part of the Czech Republic near Cheb.

There are several theories about the origin of the Moldavites; generally the most acceptable one is the shower of the Moldavites fell down to the peneplenized surface of the upper-most Mýdlovary formation (middle Tortonian) and of the weathered crystalline basement. Primary Moldavites were never found in the strewn fields, they occur only in the repositioned eluvium.

Besednice, Chlum nad Malší and Dobrkovská Lhotka belong among the most valuable moldavites localities. The largest specimen weighted 265.5 grams was found in Slavice.

Somebody believes that moldavites posses a very high content of cosmic energy and from this reason the moldavites are very popular.

Classification of moldavites

  1. Moldavites deposits

According to published work [2] moldavites deposits are divided to the four classes:

1) Upper Miocene sediments.

In this period only local depressions were filled by sediments, the moldavites were transported on the short distance. The shape of the moldavites is angular or sub angular (rare) with the strong corrosion and the emphatic sculpture. Sediments thickness is relatively small, from 0.5 to 2 metres. Typical localities are Besednice, Vrábče (Nová Hospoda), Bukovec and Borovany but these sites are relatively poor. It is the oldest type of the moldavites sediments.

2) Pliocene and Pleistocene sediments with the moldavites.

Sandy-gravel sediments come from the fluvial or the fluvial-limnic environments, the boulders are suboval or oval with the respect to the length of the transport. The moldavites posses a round shape with a good briliancy and they are deeply corroded. Thicknesses of this gravel sand beds are locally up to 12 metres. These sediments are typical with the rusty red colour which is caused by the precipitation of goethite. Typical deposits are Ločenice, Chlum nad Malší, Koroseky, Milíkovice and others.

3) Slope loams and waste rocks of the Quaternary age.

These sediments always contain transported the moldavites on the short-distance. Soils are brown or dark grey, strongly limy. The moldavites occur near Brusná, northern border of Lhenice and others.

4) Aluvial deposits in the vicinity of the present rivers.

The moldavites were mainly distributed on the north of Bohemia. Since the transport of them was long the shape is oval with the matt surface. The age of these terrace sediments responds to Holocene or the end of the Pleistocene period. The typical occurrence of these beds is gravels of the Nežárka River, near Veselí nad Lužnicí.

 

 

  1. Partial strewn fields’ classification

The chemical composition of the fallen moldavites to the South Bohemia and Southwest Moravia during Upper Miocene is not the same. This inhomogeneity was preserved among the all moldavites deposits due to the moldavites redistribution from fallen areas during the Pliocene and the Quaternary age. The main strewn field can be divided into three partial strewn fields according to the colour, the maximal projection sphericity, the chemical composition and the lechatelierite content.

  1. a) Radomilice region in the South Bohemia.

The Radomilice moldavites are typical by the pale green or bottle green colour; values of the maximal projection sphericity are relatively high. The value of SiO2 is the highest from all known localities (average 83%); the content of iron, Al2O3 and alkali is very low. The occurrence of the air bubbles and the lechatelierite is very low.

  1. b) The other deposits in the West and South Bohemia.

The moldavites are mostly bottle green coloured, the average content of  SiO2 is around 80% with the flat shape and low values of the maximal projection sphericity, include great amount of air bubbles and the high content of the lechatelierite. It is a transient member between Radomilice and Moravian group.

  1. c) The Moravian deposits.

The colour of the Moravian moldavites varies from the olive green to brown, the content of SiO2 is around 79%, values of the maximal projection sphericity are quite high and content of the lechatelierite and the air bubbles is low. The chemical analysis showed the higher content of Al2O3 (approx. 10.8%) and total iron (FeO ~ 2.8%), the values of CaO and MgO are lower than previous groups. The content of iron slowly increases from the Radomilice area to the Moravian deposits, the same situation is in the group of rare earth elements as Hf or Sc.

 

LIST OF THE MAIN MOLDAVITES DEPOSITS

South Bohemian deposits

Localities are situated in the territory among Prachatice, České Budějovice and Trhové

Sviny. In this area a lot of localities occur with different resources of the moldavites, some of them are mined by private companies or black miners, especially Chlum nad Malší - Nesměň, Jankov, Dobrkovská Lhotka, Nová Hospoda and others.

Koroseky – it lies 10 km southwest from České Budějovice. The moldavites were transported on the short distance and the sculptation is very good quality. The moldavites with needles of the lechatelierite occur in the deepest beds.

Besednice – it is situated approximately 2 km southwards from Nesměň (Figure 1.). Specimens with deeply matt shiny sculpture come from this locality. The moldavites are bigger than other localities, but good findings are unusual. The specimens from this locality are highly valued by collectors.

Figure 1. Besednice – Stoh deposit.

Figure 1. Besednice – Stoh deposit.

 

Nová Hospoda – locality is situated 1 km southwest from Koroseky. The moldavites occur in the gravel sand of the Koroseky beds and clays and gravels of the Vrabče beds. The field is covered by a great amount of pits (sometimes flooded by water) from „black miners“. This locality produces moldavites with the very thefine sculptation without the transport markings.

Dobrkovská Lhotka – it lies 4 km on east from Besednice and 8 km south from Trhové Sviny. The Koroseky sandy gravels occur not so far from the village.  Field and adjacent forest were affected by private mining (Figure 2.).

 

Figure 2. „Black miners activities“ in the Dobrovská Lhotka – Zatáčka deposit.

Figure 2. „Black miners activities“ in the Dobrovská Lhotka – Zatáčka deposit.

Radomilice – it lies around 5 km northeast from Vodňany. The individual moldavite group was named by this village. All specimens are strongly waterworn, sculptation is infrequent. The occurence of the sculptured moldavites is unusual. The light blue-green colour is typical for this place, clear and big pieces are suitable for faceting.

Nesměň – this area is located in Koroseky sandy gravels 18 km southwards from České Budějovice. Because the moldavite bearing stratas are situated in the fields between Nesměň and Chlum nad Malší, the locality is sometimes named as Chlum nad Malší deposit. The active private mining occurs in all parts of this area, industrial mining is allowed in the sandy pit in the western part of the Nesměň deposit. Very nice moldavite bearing sediments layers are uncovered in this sandy pit.

Slavče – locality lies 12 km on the southwest and the great amount of excellent sculptured and big specimens (above 90 grams) occur there.The deposit was exploited by private miners in 2004 and there is no possibility to find the nice moldavite at the present time.

 

Moravian deposits

The area of the occurence fills the space among Třebíč, Moravské Budějovice and Brno. The moldavite bearing sediments form small isolated islands with their very low content. The Moravian localities there is a very small quantity of the moldavites.

Třebíč – the moldavites occur in the small island of the Tertiary age sediments at the south border of the city.

 Slavice – it is located 3 km southwards from Třebíč. Few small places of the moldavites bearing sediments are situated around this village.

 Slavětice – a set of the discontinuous gravel islands lies between Dalešice and Dukovany. It is possible to find the moldavites with the deep sculptation in the deeper beds. The locality was exploited and new findings are very unique.

 

West Bohemian deposits

The moldavites occur in the gravel sand of the Vildštejn formation (Pliocene), rarely in the younger sediments in the vicinity of the Jesenice dam near Cheb. The first findings were caried out on the banks of dam. The moldavites are dark bottle green coloured with the high briliancy and the good sculptation. The range of the strewn field was not known yet and other localities will be probably discovered.

 

Dřenice – the moldavites occur in the local sand pit northward of the village. The weight is relatively low; the weight of the biggest stones is about 25-30 grams.

 Obilná –there is relatively great sand pit with ocassional mining activities in the top of the small hill between Obilná and Nebanice. There is a thick layer of the gravel sand with the transported moldavites. The weight is lower than in the previous locality.

 

Figure 3. Detailed map of the moldavite deposits. Legend: black square- West Bohemian deposits, black circle - South Bohemian deposits, black star – Moravian deposits.

Figure 3. Detailed map of the moldavite deposits. Legend: black square- West Bohemian deposits, black circle - South Bohemian deposits, black star – Moravian deposits.

 

Conclusions

As it is shown in Figure 4, each locality offers the moldavites with the unique shape and the individualistic sculpture. The articles approprieted to the classification and description of the moldavites localities was not published for long time. From this reason, in this article I tried to shortly explain the moldavite deposits classification and individual moldavites localities with their specifications.

 

 Figure 4. Moldavites from the South Bohemian and Moravian localities. Upper line from the left: Besednice – Dobrkovská Lhotka – Chlum nad Malší – Slavče, bottom line from the left Slavče – Kojetice (Moravia) – Dalešice (Moravia).

Figure 4. Moldavites from the South Bohemian and Moravian localities. Upper line from the left: Besednice – Dobrkovská Lhotka – Chlum nad Malší – Slavče, bottom line from the left Slavče – Kojetice (Moravia) – Dalešice (Moravia).

 References

  1. Okeefe, J.A., Adams, E.W., Baker, G.V., Barnes, E., Chao, E.C.T., Cohen, A.J., Friedman, I., Pinson, W.H., Schnetzler, C.C. and Zähringer, J.: Tektites, University of Chicago, Chicago, IL (1963).
  2. Bouška, V.: Geology of the moldavite-bearing sediments and the distribution of moldavites, AUC – Geologica 1, Praha (1972) 1.
  3. Větvička, I.: Inhomogeneous moldavites: the dependence of sculpture on chemical composition and glass flow structure, Journal of non-crystalline solids, 323 (2003), 34.