The suspect entered Pacific Precious Metals, at 420 Miller Ave., at about 10:15 a.m. and forced the store's employees to open the safe, Sgt. Michael Lane said.
The man was armed with a black semi-automatic handgun.
He took the cash and ran toward the Homestead Valley area, leading police to conduct a two-hour search, Lane said.
Units from Sausalito, Mill Valley, Tiburon, and the Marin County Sheriff's Office assisted, but the search was called off at about 12:15 p.m., he said. The sheriff's office also provided air support.
No one was injured in the robbery, Lane said.
The suspect was described as a light-skinned black or Hispanic man, about 6 feet 3 inches tall and 230 pounds, wearing jeans, white surgical gloves, and a black sweatshirt and mask.
A clerk who answered the phone today at Pacific Precious Metals directed all questions to police.
The store buys and sells gold, silver and platinum pieces, according to its website.
It was closed today while employees assisted with the investigation, the clerk said.