Comments Off on Excursion to Slanské a Zemplinské vrchy 2024
The excursion took place from 24.4.-28.4.2024 in the locality of the neovolcanic Slanské vrchy mountain range, which extends in the eastern part of Slovakia east of the city of Prešov and with its length of 100 km extends to the territory of neighboring Hungary. The Slovak part of the mountain range consists dominantly of andesite stratovolcanoes reaching heights from 800 m.a.s.l. up to 1092 m.a.s.l., which stretch in a crescent-shaped chain from north to south. They were formed at the fault interface between the tectonic units of the Západní Karpaty (gemerikum, fatrikum) in the west and hard-to-classify units in the east – zemplinikum, Pozdišovsko-Inačovská unit. The first magmatic activity is dated to the Lower Miocene as a result of the Alpine orogeny. The well-recognizable stratovolcanoes include, from north to south: Šťavnica, Zlatobáňský, Makovica, Strechovy vrch, Bogota, Hradisko, Bradlo and Velký Milič. During their formation, parts of them also underwent significant hydrothermal transformation, during which ore and opal mineralization were established.
some visited localities:
Zlatá Baňa – Zlatobansky stratovolcano – 140 types of minerals described -polymetallic (Mo-Cu-Pb-Zn-Ag) and antimony mineralization – antimonite, amethyst, bournonite, boulangerite, metastibnite, cinnabarite, galena, pyrite
Fig. 1 – Zlatá Baňa locality
Dubnik – the southern part of the Zlatá Baňa stratovolcano – the formation of mineralization in andesite lava flows by post-magmatic hydrothermal activity – significant deposit of opals (precious, milky, hyalit) -historical mining of cinnabarite as an ore of mercury
Fig. 2 – Dubnik precious opal
Herlany -Strechový vrch stratovolcano – the famous mäsovy opal of a brown-red color
The next part of the excursion took place in an elevation formed by Permocarbon continental sediments with anthracite and thick layers of tuffs – the Zemplinské vrchy. It is a synclinal structure of a complex structure consisting mainly of highly metamorphosed rocks (mainly gneisses, amphibolites).
Byšta – Brezina -near the Velký Milič stratovolcano – agates, chalcedony
Velká Trňa – the western slope of the Zemplinské Vrchy -Anthracite
Fig. 3 – Excursion checking the geological map in the field
Comments Off on SGA Student Chapter Prague autumn field trip to the Ore Mountains, Czech Republic (petrological overview, mining history, and current mineral deposits)
Jan Kamenský1,2, Jan Kulhánek1
1Faculty of Science, Charles University, Prague, Czech Republic 2Czech Geological Survey, Prague, Czech Republic
The SGA Student Chapter Prague honours its long-standing tradition of organizing an annual autumn field trip, and this year was no exception. Scheduled for late autumn (November 17–19, 2023) the trip was strategically planned to allow the participation of first-year bachelor geology students. Our destination of choice this year was the captivating mineralogical sites and historically significant localities of the Ore Mountains in the NW Czech Republic. Sixteen students participated in the excursion, led by chapter advisor Dr. Jan Kulhánek and president Jiří Klepp.
Geological settings: The European Variscan Belt finds its easternmost exposure in Central Europe, shaping the Bohemian Massif. The Ore Mountains, a historically significant mining region, are situated within the Saxothuringian Zone (SZ), the SW–NE-trending belt which extends in the NW part of the Bohemian Massif (see Figure 1). The SZ is tectonically separated from the Teplá-Barrandien unit (TBU), lying along its southeastern border. Within this framework, the SZ represents the lower plate that underwent subduction beneath the hanging wall of the TBU along a prominent Variscan suture (e.g., Franke, 1989; Jouvent et al., 2022). Comprising primarily complexly over-thrusted and over-folded metamorphic nappe units of diverse metamorphic grades, the Ore Mountains exemplify accretionary wedge formation between the SZ and TBU. From the deeper levels of the subduction channel, rocks of high- to ultra-high-pressure metamorphism, such as eclogites, blueschists, and coesite- or diamond-bearing paragneisses and granulites, have been exhumed (see Jouvent et al., 2022). The Variscian and post-Variscan tectono-magmatic activities are closely associated with the formation and subsequent remobilization of the polymetallic ores in the area. The Bohemian Massif also underwent significant magmatic and volcanic activity during the Cenozoic era. Much of this volcanic activity was concentrated along the Eger Rift, aligning with the Saxothuringian Variscan suture, and constituting the northeastern branch of the European Cenozoic Rift System (Ulrych et al., 2011). Evidence of this volcanic activity is also observable in the Ore Mountains, where well-preserved remnants of Cenozoic volcanism, erupting through the metamorphic basement, form prominent hills in the surrounding landscape.
Figure 1. The schematic geological map of the Saxothuringian Zone according to Faryad & Kachlík (2013).
1st day: The field trip began at the hut at Boží Dar, an old mining town near the Czech-German border, on the evening of November 16, 2023, which served as our base for the entire excursion. The following morning, November 17th, visit of several localities followed after the broad geological introduction at the hut. Our first visit took us to Abertamy town, where we visited private collection of mining artifacts and ore minerals sourced from the surrounding localities, such as Abertamy, Jáchymov, or Stříbro.
Continuing our trip, we embarked on a brief tour of the surrounding of the closed Mauriticius mine, the oldest tin mine in the Czech part of the Ore Mountains, with its origins tracing back to the 16th century. This historical site, now open for tourists, offered a glimpse into centuries-old mining practices. Our time at the Mauriticius mine also afforded opportunities for mineralogical sampling, with notable finds including specimens of hematite and quartz (amethyst variety) sourced from the mine’s excavation sites and observation of the metasomatic process causing formation of greisens and associated tin mineralization along the veins cutting the granitic body. In the vicinity of the Mauritius mine was also possible to observe Schnepp’s pinge, a sinkhole formed atop the remnants of a former tin mine, following the steep vein planar orientation. In the vicinity of the Mauritius mine was also possible to observe Schnepp’s pinge, a sinkhole formed atop the remnants of a former tin mine, following the steep vein planar orientation.
Our itinerary then led us beyond the confines of the Ore Mountains to the significant mineralogical site of Huber Stock, situated near Horní Slavkov (GPS: 50° 8′ 19″ N, 12° 48′ 28″ E). Geologically characterized as a greisenized plutonic elevation, Huber Stock stands as a testament to the region’s diverse mineral wealth, with notable occurrences of tungsten and tin mineralization. Historical records indicate subsurface mining activities dating back to the 13th century, with a notable period of pit quarry operations from 1973 to 1976. Notably, Huber Stock boasts a rich mineralogical diversity, with 117 documented minerals, including five designated type localities, underscoring its significance in the field of mineralogy.
2nd day: Our second day of the trip began with a visit to Meluzína Hill, a prominent feature in the landscape. Comprised mainly of eclogite, a high- to ultra-high metamorphic rock, Meluzína Hill offers insights into the region’s geological history. Originating from the subducted oceanic Saxothuringian plate, the rock was subducted deep beneath the TBU plate into the Earth’s mantle before being exhumated back to the crustal levels, shedding light on past plate tectonic processes. Discussions at the site focused on reconstructing the pressure-temperature conditions that shaped these rocks, along with an examination of the “atoll texture” of garnets commonly observed in metamorphic rocks of the area.
Our journey then took us to Horní Halže, where we explored remnants of iron ore mining. Here, a small heap served as a reminder of the area’s industrial past, with quartz veins often displaying a distinct violet color, earning the site the nickname “Amethyst heap.”
Next, we visited Mědník Hill in Měděnec, where iron ore extraction occurred from the 15th to the 19th century. The site’s skarn body, associated with the polymetallic mineralization, showcased visible garnet, diopside, and magnetite grains, providing insights into the region’s mining heritage.
Finally, we arrived at Volyně u Kadaně, a forested area housing loose rocks indicative of mining activity focused on a quartz hydrothermal vein renowned for the associated fluorine and tungsten mineralization. Characterized by a brecciated and honeycombed texture due to fluorite leaching, the vein revealed small fluorite and scheelite crystals, well-recognizable under the short-wave UV light (Figure 2).
Figure 2. Photo of collected scheelite-rich samples from the site Volyně u Kadaně under short-wave UV light. Photo by A. Ignasheva.
3rd day: Our final day began with a visit to the Kovářská site, where we examined fluorite-barite veins that were actively mined in the 1970s and 1980s. Though mining activities have ceased, remnants of these veins remain, offering opportunities for mineral collection. Participants had the chance to collect specimens of fluorite and barite from surrounding mining heaps, providing tangible connections to the area’s mining history. Moving on, we also visited a reclaimed heap near Hradiště u Kadaně, focusing on collecting hematite crystals, characteristic of the area. Our excursion concluded at the Blahuňov locality, known for hydrothermal veins cutting through gneiss formations. Here, participants observed collectible fluorite-quartz specimens, with the quartz exhibiting a carnelian variety.
With our cars loaded with mineral samples, we concluded our excursion and returned to Prague, reflecting on our experiences over the past three days. Our exploration had not only yielded valuable specimens but also deepened our understanding of the mining and geological history of the Ore mountains.
Figure 3. Group photo in front of the historical mining gallery in Měděnec. Photo by J. Klepp.
Acknowledgments: We wish to extend our gratitude to the company Severočeské uhelné doly a.s. and to the UNESCO International Geoscience Programme (project ČNK-IGCP 637) for their financial support.
References: Faryad, S. W., & Kachlík, V., 2013. New evidence of blueschist facies rocks and their geotectonic implication for Variscan suture (s) in the Bohemian Massif. Journal of metamorphic Geology, 31(1), 63–82.
Franke, W., 1989. Tectonostratigraphic units in the Variscan belt of central Europe. Geological Society of America Special Paper, 230, 67–90.
Jouvent, M., Lexa, O., Peřestý, V., & Jeřábek, P., 2022. New constraints on the tectonometamorphic evolution of the Erzgebirge orogenic wedge (Saxothuringian Domain, Bohemian Massif). Journal of Metamorphic Geology, 40(4), 687–715.
Ulrych, J., Dostál, J., Adamovič, J., Jelínek, E., Špaček, P., Hegner, E., & Balogh, K., 2011. Recurrent Cenozoic volcanic activity in the Bohemian Massif (Czech Republic). Lithos, 123, 133–144.
Comments Off on SGA Keynote speaker Professor Hartwig E. Frimmel in Prague
Jan Kulhánek1,2
1SGA Student Chapter Prague 2Institute of Petrology and Structural Geology, Faculty of Science, Charles University, Prague, Czech Republic
The SGA Student Chapter Prague was honoured to host a seminar for the entire geological section of the Faculty of Science, Charles University in Prague, featuring Professor Hartwig E. Frimmel from the University of Würzburg, Germany. The lecture, held on November 3rd, 2023, drew a diverse audience ranging from bachelor students to professors, reflecting the broad appeal of the topic, “Giant Impacts and the Formation of Ore Deposits,” within the geological sciences community.
The presentation was supplemented with a succinct annotation: “Some of the largest impact sites known on Earth overlap in space with exceptional concentrations of ore deposits. This has led to speculations on a potential addition of extraterrestrial metal compounds to the Earth’s crust on an economic scale. Using the three largest impact structures as reference, the likely controls of large impacts on metallogeny will be discussed, and it will be shown that metal endowment is strongly controlled by the regional geological make-up of the crust prior to impact.”
Inviting Professor Hartwig to our faculty provided a unique opportunity not only to hear his lecture but also for students to engage with a renowned figure in the field of geology. To underscore the significance of Professor Hartwig’s contributions, we would like to share a brief overview of his biography:
Hartwig E. Frimmel, who obtained his PhD in geology at the University of Vienna, is Professor and Chair of Geodynamics and Geomaterials Research at the University of Würzburg, Germany. He is also associated with the University of Cape Town where he had previously climbed the academic ladder from lecturer to associate professor. He was leader of the Earth Science subprogram within the South African National Antarctic Program, member of the Geoscience Scientific Standing Committee of the Scientific Committee on Antarctic Research (SCAR), former president of the Society for Geology Applied to Mineral Deposits (SGA), and director of Lithoscope consultancy. He has served on several editorial boards (incl. Mineralium Deposita for the past 23 years), on the International Commission on Stratigraphy, as assessor for numerous national research funding and government agencies, and as consultant to mining/exploration companies as well as government bodies. His research interests developed over more than three decades from metamorphic geology and fluid-rock interaction to metallogenesis and economic geology. A special focus has been the study of sediment-hosted base metal and gold deposits, especially those of the Witwatersrand-type. His research output includes more than 200 articles and book chapters as well as three books.
After the lecture, an engaging discussion was organized in the meeting room of the Institute of Petrology and Structural Geology, providing students with the opportunity to further delve into the topics covered by Professor Frimmel’s presentation. Against the backdrop of pleasant refreshments, students exchanged ideas and posed questions, enriching their understanding of the subject matter and discovering more about the Prof. Frimmel broad experiences from the world. Later in the evening, a dinner meeting was organized at a local restaurant, bringing together representatives from the SGA (Hartwig Frimmel and Anna Vymazalová, members of the SGA Executive Committee, and Prague Chapter representatives) for further networking and discussions. This gathering offered an informal setting for participants to connect with SGA representatives, facilitating valuable exchanges of ideas and insights. We extend our gratitude to Professor Frimmel for his engaging lecture and enthusiastic participation in post-seminar discussions. Our gratitude belongs to the SGA, namely SGA Keynote Speaker Program, and the Geological Section of Charles University for generously supporting the organization of this event. Their contributions made it possible to host Professor Frimmel’s lecture and facilitate enriching discussions and networking opportunities, enhancing the academic experience for all participants.
Figure 1: Flyer for the event used at the Faculty of Science, Charles University.Figure 2: After-seminar discussion in the meeting room of Institute of Petrology and Structural Geology.Figure 3: After-seminar discussion during the related sport activities.
SGA je mezinárodní organizace sdružující studenty převážně ložiskové geologie. S SGA můžete navštívit místa, kam se “normální smrtelník” nepodívá, můžete cestovat po světě, poznat nové přátele a zažít skvělá dobrodružství.
Staňte se členy SGA i vy! Vaše geologické kladivo si to žádá!
Comments Off on A field-trip to the gold mining district in Jílové, Czech Republic
Václav Santolík
“Everything is functional here,” says Vladimír Pravda showing us his “office” 300 meters below ground, where we got by a minecart. He is a member of a group of enthusiasts that bought the dilapidated Jílové mines a few years ago. With his coworkers, he spends weekends on restoring the clogged stoles and abandoned machinery.
Fig. 1 – Observation of gold-bearing quartz veins in the Jílové Mine.
Gold mining has a long tradition in the Czech Republic. There are several historically famous mining districts like Jílové, Mokrsko, Kašperské Hory and Zlaté Hory. Unfortunately, all have been shut down during or shortly after the communist era. Currently exploration is proceeding at Zlaté Hory, however, the local socio-political situation does not favor any reopening of old mines.
The Jílové gold-bearing district was one of the most important areas of historical gold mining in Bohemia. The tradition of panning dates back to the period of Celtic settlement. In the 13th and 14th centuries, when gold was obtained mainly by deep mining with a total production of approximately 10 tons of gold, the Jílové district was probably the most profitable gold-bearing district in the Kingdom of Bohemia. Unfortunately, the mines with all documentation have been burnt during the husite wars in the 15th century. The profit from reopening in the 16th to 19th century and in the years 1938 – 1968 was not even close to that of the medieval times. Finally, the geological studies from the 1960s concluded that the mining would no longer be profitable.
The fame of the Jílové district may have been based on the fact that gold was often found here in the form of coarse-grained aggregates and irregular sheets weighing up to several kilograms. The gold is present in quartz and quartz-carbonate veins, often accompanied by sulfides (pyrite, arsenopyrite, etc.), tellurium and bismuth minerals, scheelite, etc. Gold-bearing deposits usually have simple mineral composition, however, 51 minerals have been described from the Jílové district – many of them are rare, often detectable only during microscopic research.
Fig. 2 – Happy visiters of Jílové Mine at the end of excursion.
After several hours under ground, Vladimír wanted to provide us with some hands-on experience. “The country rock is very hard here, therefore, dynamite was used for digging the stoles. Here is a trigger that they used: you just need to spin the arm several times and push this button when it starts to blink,” he passes a small box to my friend. After my friend pushed the button, a staggering bang froze us. “I told you everything was functional here,” claimed Vladimír calmly. “This way, please. Before the smoke and dust reaches us.”
Z důvodu špatné epidemické situace v České republice nebudeme opět členské příspěvky vybírat na vánočním večírku, který byl z tohoto důvodu zrušen. Členské příspěvky nám prosím zašlete na účet 2058839019/3030, a to nejpozději do 24.12.2021. Prosíme Vás, abyste tento termín, pokud možno dodrželi, protože příspěvky musíme odeslat do konce roku. Do zprávy pro příjemce pak vyplňte své jméno. Viz vzor níže.
Due to the bad epidemic situation in the Czech Republic, we will not collect membership fees again at the Christmas party, which was canceled for this reason. Please send your membership fees to account 2058839019/3030, no later than 24.12.2021. We kindly ask you to meet this deadline if possible, as we have to submit contributions by the end of the year. Then fill your name in the message for the recipient. See pattern below.
Vzor/Pattern
· účet/account: 2058839019/3030
· cena/price: 260 Kč (10 euro) for students, 60 euro (1560 Kč) for non-students.
· zpráva pro příjemce/message for receiver: Vaše jméno/Your name
Nejste ještě členy SGA? Přidejte se k nám! Stačí vyplněnou přihlášku poslat našemu pokladníkovi na email (k.fizkova@seznam.cz) a zároveň poslat členský příspěvek na již výše zmíněný bankovní účet.
You are not a member of SGA? Join us now! Send filled application to our treasurer on email (k.fizkova@seznam.cz) and send membership fee on already mentioned bank account above.
Přihláška pro zájemce/Application form for new members:
Comments Off on Fieldtrip report: Zlaté Hory deposits and history of mining
Fig. 1: Participants of the fieldtrip. Photo by V. Santolík.
At the end of October 2021, the SGA student chapter in Prague held a three-day autumn excursion focused on a mining district Zlaté Hory in Jeseníky mountains and its surroundings. The area is composed of Variscan metamorphic rocks like phyllite, micaschist, paragneiss, orthogneiss, amphibolite and limestone, which were formed from Cadomian (~570 Ma) to Variscan (~300 Ma) times. The polymetallic VHMS deposit occurs in metamorphosed Devonian formations and is currently a matter of exploration for possible gold mining.
1st day. History of Au, Fe and Mo mining in the Zlaté Hory region.
The first day was focused on surface signs of previous mining and was lead by Dr. Josef Večeřa. These are dominated by placer mining marks like pits, hollows and canals as well as underground mining marks like pits and adits. The researchers were able to define three stages of mining based on different mining techniques – medieval, modern and 19th century. Interestingly, the different stages are commonly seen at a single locality. For example, in Hláska forest near Ludvíkov village, there are several pits following a single ore bearing structure and depending on the distance between particular pits, it can be inferred, whether they correspond to the medieval or modern period. Consequently, we visited a locality near Vidly village where we found several minerals related to iron ore which was mined until 18th century, including magnetite, hematite, specularite and jasper.
2nd day. Minerals collecting in mine Zlaté Hory – west; “Blue drift”.
On the second day, we went down into the Zlaté Hory – west mine, where the current exploration takes place. The walk to the end of the drift was nearly 4 km long, unfortunately the oxygen level detector did not allow us to stay there for a longer time and search for minerals. However, during the 4-kilometer walk we still managed to find several appealing minerals, for instance pyrite, galena, sphalerite, cerussite and copper. On the way back, we entered the “Blue Drift”, which is called blue for the intriguing blue colored allophane covering the walls. After a few hours in the mine, we visited local museum with a nice exposition of minerals and rocks found in the area.
Fig. 2: Azure blue allophane covering walls in the “Blue Drift”. Photo by V. Santolík.
3rd day. History of mining – open-air museum.
On the third day morning, we visited an outdoor museum dedicated to old miners and old mining techniques. We learned about their lifestyle and tools they used for daily life as well as the methods and equipment applied for gold obtainment. At the end, we were encouraged to find some gold with a gold washing pan in the arranged containers with sand and water. The most adventurous of us could not resist despite the freezing water and managed to find a few gold grains. Finally, with minds full of new experience and bags full of new minerals, we returned back home.
Fig. 3: Gold mining open-air museum in Zlaté Hory. Photo by V. Santolík.Fig. 4: Collected quartz sample with a native gold. The biggest gold has a size of 200 µm. Photo by M. Tuhý.
Děkujeme IGCP 682 – MINE TAILING REVALORIZATION (Duration: 2019-2021) za finanční podporu, která přispěla k organizaci této exkurze / We thank IGCP 682 – MINE TAILING REVALORIZATION (Duration: 2019-2021) for its financial support, which helped to organise this excursion.
Comments Off on Obnova členství/Renewal of membership
*English version see below
Kvůli pandemii COVID-19 členské příspěvky letos nebudeme vybírat na vánočním večírku (žádný se konat nebude). Členské příspěvky nám zašlete na účet a to nejpozději do 30.12.2020. Do zprávy pro příjemce pak vyplňte své jméno (pokud jméno nevyplníte, peníze propadnou do pokladny SGA). Vzor viz níže.
Due to pandemic situation we are not able to take out money for prolonging your membership on christmass party (there won´t be any). Send us your membership fee on our bank account (pattern see below) by 30.12.2020. Into the message for receiver fill your name (in the case you won´t do so, money money will be added to SGA account).
Vzor/Pattern
účet/account:2058839019/3030
cena/price: 260 Kč (10 Euro)
zpráva pro příjemce/message for receiver: Vaše jméno/Your name
do/by 30.12.20 !!!
Nejste ještě členy SGA? Přidejte se k nám! Stačí vyplňenou přihlášku poslat našemu prezidentovi na email (jaromers@natur.cuni.cz) a zároveň poslat členský příspěvek na již zmíněný bankovní účet.
You are not a member of SGA? Join us now! Send filled application to our president on email (jaromers@natur.cuni.cz) and send membership fee on already mentioned bank account.
Přihláška pro zájemce/Application form for new members:
Štěpán Jaroměřský; Karolína Fizková; Jan Šulc; Štěpán Dvořák; Marek Tuhý
Faculty of Science, Charles University, 128 43 Praha 2, Czech Republic; Corresponding author E-mail address: jaromers@natur.cuni.cz
Fig. 1: Ongoing lecture; Photo by Štěpán Jaroměřský
On 30th July was organized, despite some restrictions caused by the pandemic, excursion to South Bohemia. 15 Chapter members took part in this 1-day excursion. The expert interpretation was led by Mgr. Miloš Faltus, Ph.D. (Fig. 1). The aim of the excursion was to introduce the participants to the Czech rarity in the form of tectite called Moldavite. As one of the few people we were given the opportunity to look into the sand pit (Fig. 2), which is located between the village of Chlum and Ločenice. This sand pit is mainly used for sand mining, but its secondary product are the Moldavites (Fig. 3). It is the only company in the Czech Republic that has permission to officially mine and then sell Moldavites
Fig. 2: View of the sandpit; Photo by Jan ŠulcFig. 3: Active treatment plant; Photo by Jan Šulc
The first discovery of Moldavites was in 1787 by Dr. Josef Mayer from Charles University. He had thought of them as glass of volcanic origin. They were named after the Vltava River, around which the first findings were located. Later, the concept of Moldavite was introduced from German Moldau (Vltava). As similar glasses were later found more widely around the world, the common international name of tectite (from Greek tectose – fused) was also used for them. Generally they are vitreous bodies, which usually have dimensions of several centimeters and a weight of several units up to tens of grams. Tectites can be found all over the world, but Czech Moldavites, unlike others, have a transparent light or dark green colour.
Today, the most likely and widely accepted theory of the formation of Moldavites is considered to be the impact of a meteorite on the surface of the Earth some 14.5 million years ago. This impact occurred in the area of today’s so-called The Ries crater between Norimberk, Stuttgart and Munich. Today in the centre of this crater lies the city of Nördlingen. The Ries crater is 24 km in diameter. The meteorite impact occurred at a speed of about 20 km/s, at an impact angle of 30-50 °. During the collision with the Earth, a huge amount of energy was transferred, resulting in the crushing, melting and evaporation of rocks at the point of impact as well as a separate cosmic body. There was a cloud containing gaseous, liquid and solid phases, the main part of which was directed to the East. When the initial high temperature and pressure dropped, the silicate melt solidified so quickly that the individual mineral components did not fully crystallize to form silicate glass. This was particularly the case in the area of southern Bohemia and southern Moravia in the vicinity of Trebic. The range of the vltavins from Ries crater to southern Bohemia and southern Moravia was 200-450 km. It is estimated that the total weight of all fallen vltavins would be about 3000 tonnes.
Fig. 4: Currently found moldavite; Photo by Jan Šulc
South Bohemian Moldavite is characterised by its light – dark green colour. This is different from the Moravian ones, which tend to be in brown colours. Very rarely was also discovered bicolor moldavites, probably due to the combination of two distinct moltens before impact. Chemically, it is silicate glass, except for SiO2, which is 70-80 % represented in moltens, we can find Al2O3 in the composition. MgO, CaO or Fe oxides. The hardness varies between 6 and 7 of Mohs scale
Macroscopically, they have a very peculiar appearance and they are mostly in the shape of balls, sticks, droplets, also rarely for heart or hedgehog shapes (Fig. 5). A great interest is the sculpture, which occurs mainly on the Moldavites from southern Bohemia. This is the name of the surface of the individual samples, which has been disturbed by the acids contained in the soils. These acids then stick to the surface of the Moldavite over time, resulting in a certain wrinkling of the surface, which is quite valued. Moldavites also contain a number of inclusions, which take the form of closed-gas bubbles. Because the Moldavite is chemically very close to the glass, it is sometimes difficult to distinguish the cutted Moldavite from the cutted green glass.
Fig. 5: Rare hedgehog Moldavite form; Taken over: http://observatory.cz/static/vystavy/vltaviny/4-vltaviny.php
The sand pit, which we visited as part of our excursion, belongs geologically to the South Bohemian basins, where sedimentation began during the Cretaceous period and continued until the Tertiary. The basins are composed primarily of fluvial and lake sediments. In the visited sand pit we find Moldavites in the Domanín formation, in the Korosec series, in sands to gravel with clay inserts. Moldavites are a rare mineral, and a lot of people want them to make money. In most cases, they dig even a few meters deep pits (Fig. 6) to get into the layers that contain the Moldavites. Unfortunately, this intervention often destroys nature, natural root systems and endangers animal safety. This problem has been solved for several years and is likely to be solved by extracting all layers with Moldavite findings (except fields) followed by rehabilitation to the original natural conditions.
Fig. 6: Consequences of illegal mining; Photo by Jan Šulc
The whole excursion was a great success and we would like to thank the owner of the sand pit Ing. Viktor Weiss, who allowed us to enter the normally inaccessible area. We would also like to thank Mgr. Miloš Faltus, Ph.D., who gave us a professional lecture and last but not least, we would like to thank the entire SGA for our long-standing support and favor
Baier, J. (2009). Zur Herkunft und Bedeutung der Ries-Auswurfprodukte für den Impakt-Mechanismus. Jahresberichte und Mitteilungen des Oberrheinischen Geologischen Vereins, 9-29.
Baier, J. (2007). Die Auswurfprodukte des Ries-Impakts, Deutschland. Verlag Documenta Naturae.
Vand, V. (2009). O původu tektitů a vltavínů. Pokroky matematiky, fyziky a astronomie, 54(1), 23-32.
Řanda, Z., Mizera, J., Frána, J., & Kučera, J. (2008). Geochemical characterization of moldavites from a new locality, the Cheb Basin, Czech Republic. Meteoritics & Planetary Science, 43(3), 461-477.
Skála, R., Strnad, L., McCammon, C., & Čada, M. (2009). Moldavites from the Cheb Basin, Czech Republic. Geochimica et Cosmochimica Acta, 73(4), 1145-1179.
