Larry Overman, a professor of chemistry at the University of California-Irvine, said he and his colleagues are stumped by the igniting rocks, despite the "phosphorus substance" found on two of the stones by the Orange County Health Care Agency, the Los Angeles Times reported Friday.
The rocks caught fire in the pocket of a 43-year-old San Clemente woman after they were found on San Onofre State Beach by her children during the weekend. She remained hospitalized Friday with second- and third-degree burns.
"It's pretty implausible," Overman said. "I can't think of a scenario of chemicals on the beach that would have the properties that are described."
Tricia Landquist, a spokeswoman for the healthcare agency, said the rocks have been sent to a state lab for further testing.