Vancouver police have a Christmas whodunit on their hands after thieves made off with a rare gemstone worth half a million dollars during a weekend break-and-enter.

The massive $500,000 opal-like gem was stolen after the front window of a jewelry store in the city’s Gastown district was smashed in early Friday morning.

The 11-inch ammolite, made up of the fossilized shells of extinct marine mollusks known as ammonites, contains the same mineral that makes up pearls.

Ammolite is the official gemstone of Alberta, which means the federal government must approve an application before it is removed from the country.

Anyone with information about the theft at 313 Water Street is asked to call Vancouver police.