这种独特的宝石是极其稀有的，可以说是万中无一的珍品。

This unique gem is extremely rare, truly a ___one-in-a-billion treasure.

她独特的艺术风格使她在当代画家中是十亿里挑一的。

Her unique artistic style makes her a ___one-in-a-billion among contemporary painters.