Diving the Slovak Opal Mines

14.09.2017 08:09
Kategorie: News

Deep inside the Gem

The precious opal was discovered in the middle Ages and its name comes from the ancient Indian word "Upala" which means ‘precious stone’. Unlike other gems, opals do not form crystals. Their amorphous silica structure diffracts light and deep inside themselves they reveal the color of all gems.

Gallery 1 here

Linked with destiny

The oldest written notions date back to the 5th century BC, when an opal gem was mentioned in a poem of the Greek poet Onomakritos. Throughout the period of the Roman Empire opal was adored by the ancient Romans, some 200 years before Christ.
An important description of opal is that of Caius Plinius Secundus, better known as Pliny the Elder, a Roman author, naturalist and naval commander who lived in first century A.D. In his work Historae Naturalis Libri XXXVII he wrote: "Made up of the glories of the most precious gems, to describe them is a matter of inexpressible difficulty. For there is amongst them the gentler fire of the ruby, there is the rich purple of the amethyst, there is the sea-green of the emerald, and all shining together in an indescribable union."

The Roman senator Nonius was so obsessed with the beauty of his opal ring that he chose living in exile rather than giving up his precious in favour of emperor Marc Anthony. Napoleon Bonaparte brought a large, 700 carat heavy, black opal named ‘Burning of Troy’ as a gift to Empress Joséphine Beauharnais.

Similarly, at a later point of time, the opals played important figures in the history and most likely these were mined in the area of Slanské hills, as the site was until the half of 19th century the only major opal mine in the world. Since the middle ages opals were believed to conceal within themselves a mysterious healing power, energy supply, happiness, health and love. Later their reputation takes a darker turn in Sir Walter Scott’s novel Anne of Geierstein. After the novel was published in 1829, the stones were associated with bad luck and death, by some signified as evil eyes.

Slovak Opal Mines

The first written mention of extracting opal gems in the area of Slanské hills dates back to 1597. It is an authorization issued by Emperor Rudolf II for the maintenance of the mines for Albert Magnus of Wroclaw which constitutes written evidence.

Gallery 2 here

It was however the well-known Viennese jeweller Samuel Johann Nepomuk Goldschmidt and his family who brought the opal from this region to the peak of its fame in the years 1845-1880.

Nowhere in the world, and at no point of history, was opal mined using a mining method at such a large scale as it was at this site. Already 150 years ago about 25 thousand carats of opal a year were mined in this location, just as much as it is currently mined in Australia using surface mining method.

From local underground the world’s largest piece of precious opal has been brought to the daylight some 240 years ago, weighing 3,035 carat (594 g). Its value was estimated at half million USD. Due to its typical play of colours it was named the gem Harlequin and was a part of Austro-Hungarian Imperial Jewels, currently located in the Natoural History Museum in Vienna.


Slovak Opal Mines are located in the eastern Slovakia near Prešov, in cadastral area of Červenica. More than 22 km, seventeen levels of tunnels, shafts and adits were manually excavated in the volcanic hills, some down to a depth of 150 meters. Five lowest levels were flooded. The area is a protected region of the country and the mine itself a protected deposit area. In the biggest boom of opal extraction more 350 workers and up to 13 grinders were employed in the mine. Today sixteen species of bats are the only inhabitants of cold dark tunnels.

The underground

The portal Jozef lies on a small meadow beneath a ripe deciduous forest. Kilometres of excavated tunnels lead from dark to the surface and end with a number entrances and downcasts. Some are known and visited occasionally, while the others are forgotten and in the surrounding forest they peacefully exhaust the cold smell of the past. Nowadays Jozef is the only one that is used as an entry to the underground.

Gallery 3 here

Trees teams in autumn colors. As a visitor enters the underground, the atmosphere changes dramatically. Behind heavy thick wooden door, pleasant warm breeze with the smell of fallen leaves is replaced by heavy humid 4°C air. The hundred years old nicks of mattock are still visible on colorful walls when walking through number of horizontal tunnels. Divers walk with heavy equipment on their back. They follow an experienced guide, change the directions, change the shaft, enter another tunnel. Finally, muddy stairs bring them down to the lowest unflooded level. Entrance to cristal clear water is now just around corner. Without Peter, the way out would be lost.


Divers warm up nicely when carrying their heavy rigs and stages 40 vertical meters down to the small entry pool, however the first splash of 4°C water brings them to cold mode. It takes a few fin kicks to pass through the murky waters disturbed while kidding up, but once the view opens up, the thoughts about cold disappear. There is just a pure pleasure of observing some of the most intense play of colours a cave diver can see. The walls covered in shades of purple, red, orange, white flank long tunnels filled with clear water. Slovak opals are highly prized at the world markets for their opalescence (perfect play of colours) but now the connection between the source and result is clear.  As the predominant color changes dramatically from one room to another, it automatically evokes the variations of color in opal gem. Here, in the lowest levels of the mine, the best quality opals have been found.

In the endless corridors, the traces of human mining work such as old ladders, equipment, tracks, and constructions have been left. Here the time has stopped some hundreds of years ago. Considering that every piece, every part of equipment around, is more than 100 years old, ads a smell of the history to every breath. One can almost see the workers back in 1918 leaving the tools on the floow knowing that there is no working day tomorrow. But it is the mine walls, which attract diver’s eye everywhere he moves. Whereas over centuries the walls in dry part have been contaminated by constantly dripping water containing various compounds, the acidic water in the flooded parts keeps the original painting clear and untouched.

The colour scheme of the walls is determined by the process of mineralization. Gravity allows rust ceiling stalactites to form, reaching several tens of centimetres in length. In some parts the decoration looks just as rich as in limestone caves. But these limonite structures are fragile and collapse easily just from touch with exhaled bubbles.

In some parts the exhaled gas remained trapped in the ceiling and creates small gas capsules. Some of them are big enough to reflect the light from diver’s torch and create a glistening sheet on the floor and colourful walls. When more light sources are combined and the gas capsules move, it results in a light play that is even more difficult to describe than describing opal itself.

Hundreds of tons of volcanic material was brought up to the surface using railways but even more useless material was stored in the dead tunnels. Whereas the tunnel walls are stable, the artificial walls created with drained material mean potential threat. When these collapse and they occasionally do, the rocks obstruct the tunnel, smother the guide line and leave the diver in zero visibility.

The water is extremely cold, 3-5 °Celsius and it is strongly mineralized with mildly acidic pH which emphasizes the feel of cold. The main vertical mining shaft called Fedö connects two flooded floors and used to be so called trachea of the lowest levels. The iron rails are covered in a sheet of white cheese mould. In some places they connect and then disconnect again in several directions. A white mist floats over the railways like a morning haze disappearing in black tunnel. Miners pushing the mining trolley are expected to show up any second. Although it feels like exploring a cave, the fact that all spaces have been created by human hand, evoke memories of those who used to walk these corridors long time ago.

With many thanks to Martin Strmiska for the Script and Pictures