Lil Yachty's new chain will have people seeing double ... it's a diamond-encrusted replica of his own mug.

Yachty worked with Gabriel Jacobs, owner of Rafaello and Co., on the piece. Gabe's shop snapped the pic and used it to create the chain and it's clear he paid attention to detail.

It's over 100 carats and took over a month to make. All the diamonds had to be sourced because they're "natural" ... meaning none of them have been artificially colored. Explains the stiff $150K price tag.

Gabe says he's about 95% done. He still has to add Yachty's signature braids into the mix, but plans on hand-delivering the chain to him by the end of the week.