The precious opal was discovered in the Middle Ages and the name comes from the ancient Indian word "Upala" which means ‘precious stone’. The opal structure is amorphous (does not form crystals). The unique colouration often referred to as a ‘play of colours’, makes each piece an original.
Opals are also sometimes named The Kings of Gems. It is integral to the world's top jewellery and gems. It has one specific feature; it is a stone that reveals in itself the colours of all gems. Opal is classed among the precious stones and can have up to 60 shades of colour. It is precisely for these properties that magical properties had been, and still often are, attributed to it. Slovak opals are highly prized at the world markets for their unique features. They excel with their opalescence (perfect play of colours).
It is at this site that the world’s largest piece of precious opal was discovered, some 240 years ago (in 1771 or 1775), weighing 3,035 carat (which is approximately 600 g) and its value was estimated at 700 thousand NLG, which is now the equivalent of more than 30 million euros. Due to its typical play of colours they named the gem Harlequin (but also Vienna Imperial Opal) and it is currently located in the Natural History Museum in Vienna. The opal named Monarchy, a gift to the Royal mineralogical cabinet, had a troubled history dating back to 1803. It was lost from the Natural History Museum in Budapest in an extensive fire during the Hungarian Revolution. Another unique piece is called Isabella’s necklace, a jewel mounted with Slovak opal gems, which was a gift from John Zápoľský to his wife in 1540 (it can be found amongst the collections in the National Museum in Budapest). In 1881 the city of Budapest donated a necklace mounted with opal gems in combination with brilliants to Štefánia, Princess of Belgium, the wife of Crown Prince Rudolf on the occasion of her coronation. This jewel is still stored in the Schatzkammer in Vienna. One of the last large opals found is called ‘World War’ from the year 1914, weighing 108 karats. To illustrate, the value of an opal gem weighing over 100 carats is nearly one million US dollars.