It was just a rock retrieved off a suspected 18th century shipwreck two miles off St. Augustine.

But Chuck Meide thought there was something special inside the lump scooped from the sand about 30 feet under the waves. So the head of the St. Augustine Lighthouse and Museum's Archaeological Maritime Program took his gut feeling to the hospital.

His gut was right. Flagler Hospital Imaging Center's CAT scanner found a well-preserved flintlock pistol with scrollwork on a wooden or ivory butt still visible after 200-plus years of submergence. Once restored, one more piece of the wreck's puzzle could be revealed, Meide said.

"There is a decent chance we would have some maker's mark on the gun to tell who the craftsman was," Meide said. "That could really tie in the origins of the firearm and also give us insight into the origins of the ship."

Intact metal weaponry from two centuries ago doesn't often survive, said St. Augustine archaeologist Carl Halbirt.

"You just don't find it on terrestrial sites, and if you do, you only find rusted metal, so finding something as intact as they have found is rare," Hilbirt said.

The Lighthouse Archaeological Maritime Program finds and preserves the underwater history of the nation's oldest city. The archaeology team explored the latest wreck in late 2009 and this past summer. It retrieved a 15-inch-high cauldron likely from 1740 to 1780. The flintlock was dug from a 2-by-3-meter hole.

Flagler Hospital donated its CAT scan to look inside 25 concretions pulled off this wreck. One contained a hammer head, others a small folding knife, scissors, iron hooks on a ring and a navigational divider. Meide thought another lump could be a small pistol.

"The other folks said, 'Yeah, sure,'" Meide said. "I have a history of misidentifying concretions."

But when the CAT scanner checked, cheers erupted as its barrel, mechanism and butt showed on the screen. Experts say it is probably a gentleman's pocket pistol, popular from the 1690s to the early 1800s. Its frame and barrel are probably brass where a manufacturer's name may be engraved.

"It seems likely a highly decorated item, so this would have belonged to a merchantman or an officer, and that is interesting," Meide said.

Also seen in the concretion is a metal disc or coin, a "great find" because it could help date the wreck, Meide said.

He admits they would have to be lucky to identify the ship itself, although research into the artifacts continues and more will be brought up during next summer's dive season.

As for the gun, the staff will chip away concretion using tools as fine as a dental pick, then separate barrel and mechanism from the butt to protect its wood or ivory as the metal is preserved. It may take up to two years before the pistol is ready for display.

dan.scanlan@jacksonville.com, (904) 359-4549