The world's largest sapphire was discovered in the gem mine of Ratnapura in the “Gem City†of Sri Lanka, and it was unveiled to the world not long ago.
Its weight is astonishing, reaching 1404.49 carats, which is equivalent to about 280g (less than 10 ounces). Local gemologists say they have never seen a bigger sapphire than this.
This is a type of gemstone called "Star Sapphire", which shines with six-pointed starlight and is reflected by the crystal inside.
The anonymous owner indicated to the BBC that the gem could be sold for $175 million. The BBC wired Simon Leonfern, a mineralogist at the University of Cambridge in the UK, to find out how such a gem was formed.
Such a large piece of sapphire is very rare
The formation of sapphire is a very long process. This special sapphire is formed in the rocks of the highlands of Sri Lanka. Most of the rocks are granite, which is solidified by the cooling of the molten magma and formed by the heat and high pressure.
“The granite here has been identified for nearly 2 billion years. Later, more than 500 million years ago, large-scale metamorphic rock formations were formed, in which the rocks were squeezed and reorganized. The temperature at the roots of these mountains has exceeded 900 degrees Celsius. More than 9000 atmospheres."
Sapphire may form inside the granite before it is recombined, or later when the rock is heated and compressed.
Redfern said: "In either case, the temperature and pressure change very slowly over a million years. The crystal can grow so big."
Uncut small sapphires, more common in Sri Lanka
After the gemstone is formed, it squats in the rock. The crust rises into a mountain, and the rock is lifted up and then eroded. “The rocks are then brought to the surface, sent to the river by the scouring and weathering of the rainwater, to the gemstone sands of Ratnapura.â€
Minerals such as sapphire can survive on such a journey because they are hard enough. The relatively soft rock erodes into mud and sand, which is beneficial to the riverbed formed by heavy rainfall in Sri Lanka.
Sapphire is so hard because it consists of corundum and aluminum oxide. “Corundum is a hard guy that can be used as an abrasive on sandpaper.â€
Sapphire is one of the four precious stones, and the prices of these years have been rising. In high-quality sapphire, words such as Royal blue and Cornflower blue appear at a low frequency. These high-quality sapphires have a certain impact on the value of burning if other quality indicators are the same.
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