Lil Uzi Vert was Flashing $350k Chain and Pendant at Grammys

Lil Uzi Vert didn't take home a Grammy this year ... but he dominated the bling game by rolling into the show with more than a quarter mil around his neck.

The rapper -- who was nominated for Best New Artist, but lost to Alessia Cara -- went to the Grammys donning a custom 60-carat upside-down cross wrapped in a gold and diamond vine ... hanging from an 80-carat diamond chain.

We're told Lil Uzi reached out to celeb jeweler, Elliot Avianne of Avianne & Co Jewelers, 3 months ago to get it made ... and dropped about $350k on the piece.

We're told it was finished just 3 hours before the show and hand-delivered to him -- just in time for him to walk the red carpet ... and give this hilariously awkward interview.