The rapper dropped $180k for two 50-carat diamond chains. TMZ was told it's the handy work of celebrity jeweler Elliot Avianne, who got to work fast after Big Sean hit 'em up for the VIP treatment.
The chains are sick ... instead of going with a traditional pendant, Big Sean opted for a "Don Life" ring ... one in various colors and the other black and gold.
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TMZ was told Elliot needed two months to get the job done. He delivered it to Sean at the Billboard 100 Music Festival at Jones Beach, NY.
Admire at your own risk ... in case you decide to burn your kid's college fund.
Photos: Rachel Kaplan for iHeartRadio