Opal is a form of silica with water content varying between 3 and 21%. The amorphous nature of opal leads to its classification as a mineraloid. It usually forms in the fissures of different types of rocks. Lower temperatures favor its formation. Due to the property of diffracting light, opals often take on several colors. White and green opals are quite common but black ones are rarest. Like other gemstones, opals also vary in quality and value. Some of these gemstones have achieved enough fame to be included in the list of the most precious jewels in the world. Some of the most famous opals are as follows:
The Andamooka Opal
This world-famous opal was discovered in Andamooka, an opal mining town in South Australia. John Altmann cut and polished the gemstone to its current form. It weighs 40.6 g and has been set with diamonds into a palladium necklet. Queen Elizabeth II was gifted the Andamooka Opal in 1954 when she visited South Australia for the first time.
The Flame Queen Opal
This gemstone is often regarded as the world’s most famous opal. It is a beautiful and highly attractive opal that exhibits an eye-like effect due to its unique structure. A flat raised dome of the gemstone in the center is surrounded by a deep blue-green colored band. The central part can appear as gold or red in color depending on how the stone is viewed. This opal weighs 52.636 g. The Flame Queen Opal was uncovered in 1914 at Lightning Ridge in the Australian state of New South Wales.
The Halley's Comet Opal
This gemstone holds the record of being the world’s biggest uncut black opal. The opal has been named after the Halley's Comet since the comet could be seen from the Earth in the same year of the discovery of this opal. The gemstone was uncovered at the Lightning Ridge in the Australian state of New South Wales. The Halley's Comet Opal weighs 396.50 g and is nearly flawless. The size of the opal can be compared to the fist of a person. As of 2006, the opal was priced at $1.2 million.
The Olympic Australis Opal
This precious gemstone is regarded as the world’s largest single piece of rough gem opal. It is also the most highly priced gemstone of its kind. The Olympic Australis Opal was discovered during a mining operation at an opal field in the mining town of Coober Pedy in South Australia. The gemstone was named after the Olympic Games that were being hosted in Melbourne, Australia at the time of its discovery. The opal has a weight of 3450 g and is estimated to be worth about $1.9 million.