Police are hunting for a Santa Claus look-alike after he stole a $75,000 emerald from a Midtown jewelry store.

The man — whom police described as “heavyset with a long white beard” — took a Colombian emerald from a display case at the Astro Gallery of Gems on Madison Avenue near 34th Street at 11:40 a.m. Thursday.

“He reached in, took out the emerald, and took off,” said a police source.

The theft was not discovered until after the man — who was not wearing a Santa costume — left the store.