He sold them to the government for 7.7 billion Tanzanian shillings (about R56.5 million).
Tanzanite was first found in the foothills of Kilimanjaro in 1967, and the northern Tanzanian region of Manyara is the only known place where the stones, coveted by jewellers for their remarkable violet-blue sparkle, are found.
At a function celebrating the find in Manyara on Wednesday, mining minister Dotto Biteko said the stones were the biggest ever uncovered in the country.
“Laizer is our (shilling) billionaire and let us make sure that he is safe,” he said.
“We are now moving from a situation where the small miners were smuggling tanzanite, and now they are following the procedures and paying government taxes and royalties.”
Laizer said he hoped to use the money to develop his community.
“I plan to build a mall in Arusha and a school near my home,” said Laizer.
“I thank God for this achievement because it’s the first time to get this size. When I found these, I notified government officials who valuated the stones and today they called me for payment.”
The government wrote on Twitter that the stones would be placed in the national museum.
Magufuli made a call to Laizer during the ceremony that was broadcast on loudspeakers, to congratulate him.
“This is the benefit to small miners and testifies to the fact that Tanzania is rich,” he said.
When the 24km (14-mile) perimeter wall was unveiled around the mining site, Magufuli said that 40 percent of all tanzanite produced at the site was being lost to smugglers.
Magufuli has taken multiple steps to regulate the mining sector, which has faced allegations of fraud and underreporting of production and profits.
Tanzania in 2017 introduced new regulations obliging foreign companies to give 16 percent free shares to the government.