A broke builder is set for a windfall after finding a rare Tridacna pearl while walking along a beach in Thailand.

Adisak Boonrat, 47, said he went to Ban Laem Pho beach to catch shrimp and saw a beautiful shell with a white marble-like object in Krabi province in June.

The worker kept it at home but finally took it to a jewellery store where staff said it was a rare Tridacna pearl from a giant clam.

Adisak kept it for months until he decided to put it up for sale on November 7 with the help of the local officials.

Footage shows Adisak with police as he revealed that he is the owner of a rare pearl that could fetch tens of thousands of dollars.

He said: ‘I didn't have food that day and went to the beach to find some shrimp. It was a tough day and my net was still empty in the afternoon so I just went home.

‘While I was walking at the beach, I found a large shell. I went to check it and found a marble inside. I realised it could be a pearl so I took it to the jewellery store to pawn. When I found out it was expensive, I decided to keep it home until I know what to do with it.'

The worker's pearl was 1 cm in diameter and estimated to be 20 carats. This type of pearl, produced by endangered giant clams, are extremely rare and has a high collector's value so he is expected to earn several thousand dollars from it..

Adisak said a buyer has already contacted him to make a deal but he is holding out for a higher price.

He said: ‘I found the pearl for a reason. My life has completely changed. I will only agree to give it if they offer me a reasonable price.'

The minimum-wage worker is now waiting for an institution to issue him a certificate that proves the pearl is genuine and would entertain more collectors offering to buy.

Adisak's pearl, dubbed ‘pearl of Allah' or ‘Lao Tsu's pearl' by gem enthusiasts came from giant clams or Tridacna gigas found in tropical coral rads throughout the Indo-Pacific ocean. These pearls have become extremely rare because harvesting them is illegal.

The biggest Tridacna gigas pearl was found in the Philippines worth 100million USD. It was found by a fisherman and took it home as a lucky charm, kept hidden under his bed for years. It was only discovered by authorities after his house burned down and the 34 kg pearl survived.