"They've been moved around by wind. They've been mixing with other materials. It's a big, jumbled up, fascinating mess," Squyres said.
In contrast, the newly discovered deposit is threaded into an ancient rock on the rim of a large crater named Endeavour, which Opportunity is now exploring.
"This stuff formed right here," Squyres said. "There's no ambiguity about this.
SCIENCE CHANNEL: Red Planet Puzzles
"There was a fracture in the rock. Water flowed through it. Gypsum was precipitated from the water. End of story," he said.
Both the chemistry and the structure "just scream water," Squyres added.
Scientists hope to probe other fracture-filled rocks when Opportunity heads for new ground after the Martian winter.
A similar find may be in store for the team working with NASA's Mars Science Laboratory, a new, more sophisticated rover currently enroute to Mars. The robotic probe, nicknamed Curiosity, is scheduled to land inside a 96-mile wide impact basin called Gale Crater on Aug. 6.
The crater contains a layered mound of deposits three miles high.