MARIPOSA, Calif. (October 1, 2012)—Authorities in California were looking Monday for the thieves who made off with an estimated $2 million in precious gems and gold from a Central Valley museum in a brazen daytime robbery.

The California Highway Patrol said the robbers were armed with pickaxes and threatened workers during the heist Friday at the California Mining and Minerals Museum in Mariposa.

No suspects have been identified.

The museum houses more than 13,000 artifacts, including the Fricot Nugget, a nearly 14-pound crystalline gold mass.

Investigators would not say what items were taken, but did confirm the nugget was not among them.

It's the second heist this year of rare, valuable metals in Northern California.

In February, thieves made away with large chunks of gold that were on display in a Siskiyou County Courthouse.