Witherspoon, 34, became engaged to talent agent Jim Toth on December 28 after a whirlwind romance.
The beautiful 4-carat engagement ring is an Ashoka cut set on a pave diamond and platinum band.
The shape was re-created based on the famous 41.37 carat diamond named after the Buddhist warrior-emperor Ashoka Maurya and is known for its exceptional beauty and unique cut.
"In the past year, the retro look in diamonds has been very popular," Radar Online quoted jeweller William Goldberg as telling People magazine of the design.
"It's a very elegant cut and it has an old feel to it," he stated.