Moldavite is a green glassy substance that belongs to the group of tektites - natural glasses formed by the impact of a meteorite on the Earth's surface. Moldavites are found only in some regions of the Czech Republic, Germany and Austria and are considered rare and valuable gemstones.
The origin of moldavite has been a subject of debate and speculation for centuries. There are several theories that attempt to explain how this unusual material came into existence, but the most widely accepted one is related to a meteorite crash in southern Germany about 15 million years ago. According to this theory, the meteorite melted the surrounding rocks and ejected them into the atmosphere, where they solidified into glass. This theory is supported by the chemical composition, isotopic analysis and texture of moldavites.
However, there are also other hypotheses that suggest that moldavite has an extraterrestrial origin and is a part of the meteorite or lunar obsidian. These theories are based on the unusual color, shape and properties of moldavite, as well as its similarity to other tektites from different parts of the world.
In this article, we will review some of the main theories about the origin of moldavite and evaluate their strengths and weaknesses.
Meteorite Impact Theory
The meteorite impact theory is the most widely accepted explanation for the origin of moldavites. It was first proposed by Austrian geologist Eduard Suess in 1900, who also coined the term tektites for this type of natural glass. He noticed that moldavites had peculiar pittings and wrinkles on their surface, which resembled those on many meteorites. He also observed that moldavites had a very low water content and a chemical composition similar to terrestrial rocks.
According to this theory, moldavites were formed when a large meteorite hit the Earth in the present-day Nördlinger Ries crater in southern Germany. The impact generated a huge amount of heat and pressure, which melted the rocks at the site of the collision and launched them into the air. As the molten material was airborne, it cooled and solidified into glass droplets. These droplets were scattered over a large area that includes southern Bohemia, western Moravia, the Cheb Basin (northwest Bohemia), Lusatia (Germany), and Waldviertel (Austria).
The meteorite impact theory is supported by several lines of evidence:
- The chemical composition of moldavites is similar to that of terrestrial rocks, especially those from the Bohemian Massif, which suggests that they were derived from local sources.
- The isotopic analysis of moldavites shows a beryllium-10 isotope composition similar to that of Australasian tektites (australites) and Ivory Coast tektites (ivorites), which are also believed to be products of meteorite impacts.
- The texture of moldavites is characteristic of quenched glass, which indicates rapid cooling from a molten state. Moldavites also have flow structures and lechatelierite wires (a high-temperature form of SiO2) that are typical of impact glasses.
- The distribution of moldavites is consistent with an impact origin. Moldavites are found in a strewn field that covers about 400 km by 50 km, with most specimens concentrated near the western margin of the České Budějovice Basin. The size and shape of moldavites also vary according to their distance from the impact site: larger and more spherical specimens are found closer to the crater, while smaller and more irregular ones are found farther away.
The main weakness of the meteorite impact theory is that it does not explain why moldavites are found only in Central Europe, while other tektites are found in different continents. Some researchers have suggested that moldavites are part of a larger tektite strewn field that extends across Europe and Asia, but has not been fully explored yet. Others have proposed that moldavites are related to a specific type of meteorite that had a limited distribution on Earth.
Lunar Origin Theory
The lunar origin theory is one of the alternative explanations for the origin of moldavites. It was first suggested by American geologist John O'Keefe in 1958, who also proposed that all tektites were derived from lunar volcanoes. He based his hypothesis on the similarity between tektites and lunar rocks, especially obsidian.
According to this theory, moldavites were formed when a large asteroid or comet hit the Moon and ejected molten material into space. Some of this material reached the Earth and fell as tektites, while some remained in orbit and formed the lunar maria (dark areas on the Moon's surface). Moldavites were part of the lunar material that landed in Central Europe.
The lunar origin theory is supported by some arguments:
- The color and transparency of moldavites are similar to those of lunar obsidian, which is a type of volcanic glass found on the Moon.
- The refractive index and density of moldavites are lower than those of terrestrial rocks, but higher than those of other tektites, which suggests that they have a different origin.
- The water content of moldavites is very low, which is consistent with a lunar origin, since the Moon is a dry body.
The main weakness of the lunar origin theory is that it contradicts the isotopic and chemical evidence that links moldavites to terrestrial rocks. Moldavites have a different oxygen isotopic composition than lunar rocks, which indicates that they were not derived from the same source. Moldavites also have a higher content of aluminum oxide and iron oxide than lunar rocks, which implies that they were not formed under the same conditions.
Cosmic Origin Theory
The cosmic origin theory is another alternative explanation for the origin of moldavites. It was first suggested by Russian geologist Nikolai Kudryavtsev in 1961, who also proposed that all tektites were fragments of a comet or an asteroid. He based his hypothesis on the unusual properties and distribution of tektites.
According to this theory, moldavites were formed when a large comet or asteroid broke up in the Earth's atmosphere and fell as tektites. Moldavites were part of the cosmic material that landed in Central Europe.
The cosmic origin theory is supported by some arguments:
- The shape and surface features of moldavites are similar to those of meteorites, which suggests that they were formed by aerodynamic forces during their flight through the atmosphere.
- The distribution of moldavites is consistent with a cosmic origin. Moldavites are found in a narrow band that follows the trajectory of the comet or asteroid. The size and shape of moldavites also vary according to their position in the band: larger and more spherical specimens are found at the beginning, while smaller and more irregular ones are found at the end.
- The water content of moldavites is very low, which is consistent with a cosmic origin, since comets and asteroids are dry bodies.
The main weakness of the cosmic origin theory is that it does not explain why moldavites have a chemical composition similar to that of terrestrial rocks. Moldavites have a higher content of silicon dioxide and lower content of magnesium oxide than comets and asteroids, which indicates that they were not derived from the same source. Moldavites also have a different isotopic composition than comets and asteroids, which implies that they were not formed under the same conditions.
Conclusion
Moldavite is a fascinating stone that has intrigued scientists and collectors for centuries. Its origin is still a matter of debate and speculation, but the most widely accepted theory is that it was formed by a meteorite impact in southern Germany about 15 million years ago. However, there are also other theories that suggest that it has an extraterrestrial origin and is a part of the meteorite or lunar obsidian. Each theory has its strengths and weaknesses, but none can fully explain all the aspects of this mysterious material. Perhaps further research and exploration will reveal more clues about the true nature and origin of moldavite.
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