Screw jerseys, hats and jackets ...Post Malone's repping the Dallas Cowboys in the most baller way possible -- with a $250,000 diamond chain!!!

The "White Iverson" rapper is showing off some new bling to profess his fanatical admiration for his favorite NFL team. Angel City Jewelers are the masters behind the chain and massive pendant ... and they delivered it to him at AT&T Stadium last weekend for Post Malone’s second annual hometown festival, Posty Fest.

We're told the new bling includes 3,000 stones, 9.7 carats of baguettes, 13.5 carats of sapphires and 8.7 carats of diamonds. There's also a "77" inscription on the back ... PM's favorite number.

Post Malone's fandom for the Cowboys is unrivaled. He's gotten a NY Giants fan to wear his Cowboys jacketafter winning a bet. PM's also put his money where his mouth is ... and it once cost him. Like when he handed over 20k to YG after the 'Boys fell short to the Rams.

Betting he'll never wager his new diamond chain.