21 Savage is going all out when it comes to a personalized piece of jewelry he just scooped up -- it's not only a replica of his mug ... it's dripping in diamonds. 

Gabriel Jacobs, owner of Rafaello & Co, just debuted the Atlanta rapper's new split personality pendant -- one side is Savage's face, right down to his tats. The other side is a Jason Voorhees mask ... a tip of the hat to his "Slaughter King" mixtape.

Gabe tells us it took him more than 2 months to finish the pendant. The head is covered in 100 carats of VVS grade, near flawless, natural white diamonds. That's what $125,000 will get ya!

This piece AND Amber Rose? Who's having a better summer than Savage?

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