What turns an underwater rock into a shining collection of ancient silver coins?

A few weeks of careful conservation.

Conservators from Mel Fisher's Treasures this weekend started the process that will break down the concretion that surrounds several shiny coins recovered Friday from the wreck of the Santa Margarita.

Diver Kris Goodner recognized the telltale circular shape of coins within the mass and returned with excitement to the exploration vessel Blue Water Rose.

Divers with Blue Water Ventures have spent the last four years salvaging the wreck of the Santa Margarita, which was loaded with at least 150,000 silver coins when it left Havana Harbor bound for Spain in September 1622.

The ship never made it to Spain, and a deadly hurricane ground the galleon into a sand bar in the Florida Straits. The same storm also sank the Margarita's legendary sister ship, the Nuestra Senora de Atocha, just three miles away, said Carol Tedesco, spokeswoman for Blue Water Ventures.

The Atocha relinquished much of its priceless cargo to Mel Fisher's treasure-hunting team in 1985, and the Fisher divers had first located part of the Santa Margarita in 1980.

But the treacherous currents and ever-shifting sands in the area of the Margarita wreck made early recovery efforts impractical and dangerous, and Keith Webb, CEO of Blue Water Ventures, estimates that only one-third of the silver coins have been found.

With technology evolving to meet the challenges of the environment, Webb's team became a joint-venture partner with Mel Fisher's Treasures, and successfully has taken over the search and recovery work on the Margarita site.

The most recent discovery will spend the next few weeks in the Greene Street lab, where Chief Conservator John Corcoran will X-ray the clump and then break down the calcareous concretion that holds it together.

Corcoran was reluctant to give an estimated time frame for the conservation, as he does not yet know what he is working with.

In addition to at least seven coins, whose shapes are clearly defined, the clump could contain jewelry, an iron spike or any other metal item, Tedesco said on Monday.

But the crew from the Blue Water Rose are not waiting around to find out what they found. The boat headed back out to the search site Monday afternoon to take advantage of as much nice weather as possible, Capt. Dan Porter said.

Their last dives on Friday revealed the clump of coins, as well as an ornate silver artifact, two loose coins and an arquebus, which was an early, muzzle-loaded firearm, Tedesco said.

Porter was planning to return to the same area on Monday.

"We're calling the area 'the guns and gold trail,' " he said. "And we're going to start right where we left off on Friday."

mmiles@keysnews.com