Big Sean Drops $180k for 100 Carat Diamond Chains

Big Sean is a bo$$ with shiny chains to flo$$ ... and the boss life ain't cheap.

The rapper dropped $180k for two 50-carat diamond chains. We're told it's the handy work of celebrity jeweler Elliot Eliantte, 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.

We're told Elliot needed 2 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.