Tanzanian miner Saniniu Laizer has become a millionaire overnight by selling two Tanzanite gemstones — the largest ever found in the country — for 7.7 billion Tanzanian shillings ($3.4 million), according to multiple media reports.

The stones weigh 9.2 kg (20.3 lbs) and 5.8kg, and Laizer mined them last week but sold them Wednesday at a trading event in the region of Manyara, the BBC reported.

Laizer, reportedly a father of more than 30 children, told the BBC that he planned to use the money to build a shopping mall and school in his community in Simanjiro, a district of Manyara.

“I want to build this school near my home,” he told the news outlet. “There are many poor people around here who can’t afford to take their children to school.”

He added: “I am not educated but I like things run in a professional way. So I would like my children to run the business professionally.”

Despite his newfound wealth, Laizer said he would continue to look after his herd of 2,000 cows. The small-scale miner said he would slaughter one of the cows to celebrate and that there would also be a “big party.”

Tanzanian President John Magufuli has reportedly congratulated Laizer over the phone and said the find showed the benefit of small-scale miners and “proves that Tanzania is rich.”