Moldavite

Moldavite is a beautiful green tektite that is only found in one area: the southern part of the Czech Republic, a small adjacent part of Austria and a small part of Germany. The meteorite that caused the formation of moldavite hit just northwest of present-day Munich. The crater that was created as a result is called the Ries crater.

A tektite is an impact glass, natural glass created by the impact of a meteorite. Tektites are not rare and occur in many places in the world. Characteristic of moldavite is the beautiful green colour (although brown moldavite also exists). This colour is caused by the presence of iron. The less iron, the lighter green the moldavite. With more iron, the colour becomes more brownish green. The type of iron also determines the colour. Divalent iron gives a greener colour, trivalent iron a browner colour.

Moldavite has been known for a long time, but until recently it was not known that it is a tektite. The green pieces of glass were probably already considered special in prehistoric times. For a long time it was not known where the green glass came from. All kinds of theories have been suggested and discussed. From volcanic glass to remains of old glass factories. In 1786 moldavite was first officially described by professor Joseph Mayer. At that time it was called chrysolite. It was only in the 1960s that the Ries crater was discovered. The composition of the moldavite and the subsoil in the Ries area matched, as did the dating. So the conclusion was drawn that the two must be related.

Moldavite is named after the Moldau/Vltava River because this is the area where most moldavite is found. The southwest part of the Czech Republic is the best-known location, but moldavite is also found just across the border with Austria (Waldviertel) and in a small part of East Germany (Lausitz). That is quite a distance from where the meteorite hit. The entire area where moldavite occurs is called the strewn field. During the impact, a huge amount of material was slung into the air under high pressure and temperature. It melted and then quickly solidified again. The melting process turned it into glass. Moldavite has a Mohs hardness of 5.5 – 6. When you put a piece under a microscope, you will see elongated worm-like streaks in the glass, lechatelierite inclusions. Moldavite also has so-called ‘schlieren’, these are characteristic of genuine moldavite. They are straight thin lines that were created because the material was only liquid for a very short time. It is thought that these were grains of sand that were not properly dissolved and mixed.

The typical edged structure of moldavite has nothing to do with the formation, it happened afterwards because natural acids etched the glass. Air bubbles are a common characteristic of moldavite, these are often somewhat elongated, but round bubbles are not impossible. A distinction is sometimes made between loose larger bubbles and small ones that are often close to the lechatelierite (chemically also amorphous SiO₂) inclusions.

Those air bubbles in moldavite are a study in itself. The content of these air bubbles has been investigated. In moldavite they largely consists of carbon monoxide. In addition, it contains nitrogen, hydrogen, carbon dioxide and hydrogen chloride. The percentage of carbon (C) in moldavite is very low, the carbon that is present can be traced back to an organic origin according to researchers. So to plants that grew at the place where the meteorite hit. The presence of air bubbles indicate that the glass was formed in an environment where the air pressure must have been very low (high in the atmosphere). The air pressure in the bubbles is also very low, but that is not necessarily because of the air pressure in the atmosphere. There are three theories about how air bubbles form in tektites.

The most widely used theory states that the outside of the glass cools down faster than the inside. When the inside cools down, it takes up less space than when it was warm. Which means that there is more space than glass. Logically, there will then be ’empty’ spaces in the moldavite because there is not enough glass to fill everything. These empty spaces are the air bubbles. In the air bubbles that are formed in this way, there is an almost complete vacuum. Another way in which air bubbles can form is by gas that was already present in the molten mass being released and concentrated in air bubbles in the rapidly cooling glass. The theory that the air bubbles are formed by gas from the immediate environment that becomes trapped in the glass has been investigated and this process is very rare.

Moldavite has a relatively high SiO₂ content compared to other tektites. Due to the small proportion of titanium dioxide and iron oxide, they are also reasonably transparent. The composition of the glass that moldavite consists of is attributed to the sediments of the ‘Obere Süßwasser Molasse’, the freshwater deposits that covered the area at the time of the impact. Mainly quartz-bearing sand, very little carbonate material, but a lot of plant growth. The match between deposit and moldavite composition is not 100%, but is similar enough to be able to draw this conclusion. In general, it is agreed that the substances that moldavite consists of have a terrestrial (earth) origin and moldavite is therefore not a mixture of terrestrial and extraterrestrial (meteorite) material. There are elements in it that can most likely be traced back to the meteorite, but that is very minimal and concerns fractions of a percent.

The shape of moldavite is quite variable at first glance. However, most moldavites belong to the same type of tektite, the so-called ‘splash-form’. These have various shapes that have formed during transport through the air. They can be droplets, bell shape, spherical, ellipse or elongated. Some of these shapes have formed because the pieces rotated in the air. Undamaged complete pieces of these splash-form moldavites are rare and very popular (and therefore expensive). The famous ‘hedgehogs’ from the Besednice area are among the most expensive and sought-after moldavites. This shape strongly resembles a splashed out drop, but that is not how the shape has formed. This typical structure and shape is due to weathering over the years. A second type of tectic, the Muong Nong type tectic, is a layered tectic. This is quite rare among moldavite.

Because moldavite only occurs in a very limited area, it is relatively rare. It is not newly formed anymore, so gone is gone. In recent years, the popularity of moldavite has increased enormously, partly thanks to social media. With it, the demand and the price increased. ‘Ordinary’ pieces of moldavite are usually priced based on weight, per gram or carat. Exceptional forms like complete drops or other special splash-form varieties can be much more expensive. The most popular and expensive are the ‘hedgehogs’, some pieces are offered for sale for thousands of dollars.

Fakes & frauds
Unfortunately, thanks to the online moldavite hype, the supply of fake moldavite has also increased significantly. Most fake moldavite is simply man-made green glass. Fortunately, there are a few things you can look out for when purchasing a piece.
– Raw moldavite has a matte sheen. If you see a rough piece with a high lustre, glass sheen or a greasy sheen, you may assume that it is fake.
– Every rough piece is unique. If all the pieces that a dealer offers look the same, have the same shape, that is very suspicious. Many fake pendants are flat and round, the size of a euro coin.
– Real moldavite is not cheap. This is no guarantee that expensive pieces are real, but very cheap pieces are a ‘red flag’.
– The structure is sometimes milled with a machine. This can be recognized by rougher parts in the grooves, straighter grooves and abrupt transitions. This is the most difficult form of fake to recognize, because the grooves that are made can be etched with a little acid to look more natural.
– Real moldavite has the above mentioned worm-shaped lines under the microscope, this is more difficult to imitate in cheap imitations.
– A lot of round air bubbles in a piece is suspicious.
– For polished pieces, the refractive index of moldavite is different from that of normal glass, so a refractometer can be used to determine whether a piece is real.
– Moldavite is only green and very rarely brown-green. Other colors are fake. Nowadays, red, blue, yellow and rainbow-coloured ‘moldavite’ are offered. These are all fake.
– When someone says that the piece comes from a place that is outside the known strewn field, it is very unlikely that it is real. Very occasionally pieces have been found outside the described places, but this can often be traced back to movement by water and very occasionally by people (pieces have been found during archaeological excavations of prehistoric sites).
– About ‘moldavite’ bead bracelets. Think about it for a moment… most moldavite pieces are not thick enough to carve into beads. Round beads would have to come from large (read: expensive) pieces. If you can buy such a bracelet for a few euros, dollars, pounds, you know that this cannot be right and is too good to be true.
– A ‘certificate of authenticity’ is unfortunately no guarantee of authenticity. Anyone can print a fake certificate. Unfortunately, there are a lot of meaningless fake certificates (with forged numbers from tests that are supposed to have been done in gemological laboratories). This does not only apply to moldavite, but to many more polished and unpolished stones.