Slovak Opal

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Slovak Opal – Harlequin, the largest precious opal of Europe. Collection of Naturhistorisches Museum, Vienna, Austria.

Slovak opal is a certified geographical name of precious opal mined from deposits in Slanské vrchy in eastern Slovakia. Slovak opal is a natural hydrated amorphous form of silica with variable water content (SiO2. nH2O) typical for which is its internal diffraction light which creates a plethora of colours creating large esthetical value.

Content

  • 1 Deposit
  • 2 Characteristic
  • 3 Varieties
  • 4 History
  • 5 Usage
  • 6 Pictures of opals
  • 7 Jewellery with Slovak Opal
  • 8 References

Deposit

Deposit of Slovak Opal is located in Eastern Slovakia in the Slanské vrchy mountain range, near the village Červenica (district of Prešov). Slovak opal mines are situated within the PDA Červenica I. (Protected Deposit Area). Opal is mined in Mining Site MS Červenica by the company Opálové bane Libanka, s.r.o .

Characteristic

Opal forms when fluids rich on SiO2 impregnate cracks in andesite parent rock in hydrothermal or hydrothermal-postvulcanic phase. The looks of Slovak Opal are influenced by very small gel balls with a diameter of 0.2 – 0.8 nm of cristobalite. If these balls have the right size, their surface diffracts light in the typical opalization effect. If the balls are smaller, opalization does not happen. Slovak Opal consists of 90 – 91 % cristobalite, which assures a decided production of spectral colours.

Common opal is found on several other, though less important sites in the Slanské vrchy mountain range. A list of Common Opal deposits is published in the book Opály Slovenskej a Českej republiky.

Slovak Opal is the only precious opal in Europe and Asia. That is why the geographical name is not derived from the name of the Mining Site but from the name of the country – Slovakia-Slovak. The second part of the name is the name of the mineral – opal. On October 11th 2016 the Industrial Property Office of Slovak Republic issued a certificate of Designations of origin for products and geographical indications for products. This certificate was registered by WIPO (World Intellectual Property Organization) on November 10th 2016 under the registration number 1061.

Varieties

Slovak Opal is from a mineralogical point of view the most precious type of opal – Opal AG. Based on its definition in the official gazette its differentiated into three varieties:

  • milky – the base is a white transparent and semi-transparent milky opal with iridescence in depth as well as on the surface
  • crystal – the base is transparent and semi-transparent opal with iridescence in depth as well as on the surface
  • Matrix  – is made from andesite parent rock partially sated with opal matter creating sheets and veins of opal with iridescence.

 

By constancy of water Slovak opal can be differentiated into:

  • hydrofan
  • non hydrofan

History

Slovak opal (also known as Červeník-Dubník Opal, Červeník Opal, Hungarian Opal, Vienna Imperial Opal). Slovak Opal was known worldwide since the end of the 16th century. The largest opal found was called Harlequin, , it weighed 594g, was found in 1775 and was valued at 700 000 Dutch guilders. Today it is displayed in the Museum of Natural History in Vienna. The second largest opal weighed 400ct, it was named Monarchy and the owner of the mine, Jozef Rumpler gifted it to the royal mineralogical cabinet.

Mining operations at Libanka were suspended in 1922 because of bad economical situation after the war. Operation was suspended according to edict 311/62/32844/Úsp./C/23 from 16.10.1923, document (Správa státních solivarů v Slolnohradě/Management of state salterns Slolnohrad) from 31.12.1923.

At present mining operations resumed at MS Červenica in May 2012 under the direction of Opálové bane Libanka, s.r.o., followed by surface mining operations since October 2012 on tailings pile Viliam under the name Monika. On October 11th 2016 the Industrial Property Office of Slovak Republic issued a certificate of Designations of origin for products and geographical indications for products. This certificate was registered by WIPO (World Intellectual Property Organization) on November 10th 2016 under the registration number 1061.

Usage

Slovak opal is used in goldsmithing and jewel-making. If we want to use this mineral in jewels it has to be treated first. The way the gem is cut and polished depends on the size, shape and other characteristics of the gemstone. The complex process of bevelling encompasses the readying and choice of gemstones. Bevelling the gem into the needed shape is performed by cutting, roughing, smoothing and final polishing. Opal is mostly cut into oval shapes, tears and fantastic shapes. Natural gemstones don’t always have perfect shape, sometimes small cracks may occur which is unavoidable.

Pictures of opals

Jewellery with Slovak opal

References