Workmen digging a well in a man's backyard discovered a $100 million windfall: a 2.5 million-carat sapphire cluster

• Men digging a well hauled up a 1,100-pound sapphire cluster worth $100 million, the BBC reported.
• The cluster, named the "Serendipity Sapphire," is 2.5 million carats.
• This lucky find happened in Ratnapura, known as Sri Lanka's city of gems.

Workers digging a well in the backyard of a Sri Lankan gem trader stumbled upon a 2.5 million-carat sapphire cluster, the BBC reported on Tuesday.

The lucky find was made in the southern city of Ratnapura, known as Sri Lanka's "city of gems." The cluster, named the "Serendipity Sapphire," is a staggering 39 inches long and 28 inches wide, The Nation, an English-language newspaper in Sri Lanka, reported.

Gamage, a third-generation gemstone trader and owner of the stone, told the BBC that it had taken over a year to wash off the 1,124-pound cluster, analyze the stone, and certify it.

"The person who was digging the well alerted us about some rare stones," Gamage, who declined to give his full name, told the BBC. "Later we stumbled upon this huge specimen."

What tipped him off that the find could be worth an astronomical sum was that high-quality sapphires kept chipping off while he was cleaning impurities off the rock, he said.

Experts have valued the sapphire cluster at up to $100 million, the BBC reported.

"I have never seen such a large specimen before," Gamini Zoysa, a gemologist, told the BBC. "This was probably formed around 400 million years ago."

Thilak Weerasinghe, the chair of Sri Lanka's National Gem and Jewelry Authority, told the BBC that the sapphire would likely be of interest to private collectors and museums, considering its size and value.

The Serendipity Sapphire alone could be worth a significant portion of Sri Lanka's annual gem exports.

Sri Lanka is known for its gem finds. Other large sapphires found in the country include the "Blue Belle of Asia," a 392-carat sapphire that sold at auction for $17.5 million in 2014.

Another was the "Star of India," a 563-carat star sapphire on display at the American Museum of Natural History in New York. In 1964, amateur jewel thieves broke into the museum, used a glass cutter and duct tape to open the stone's display box, and made off with it.

A Sri Lankan jewelers' organization told the BBC in 2011 that the 12-carat sapphire in Kate Middleton's ring likely came from mines in Sri Lanka.