Flaming Rocks Puzzle Health Officials

Mystery solved. Well, kind of.

California environmental officials say that they think they have figured out what caused a handful of rocks to burst into flames while in the pocket of a woman who had picked them up off a San Clemente beach last week: a highly-flammable phosphorus substance that the rocks were coated in. Experts just don't know how the substance got there.

"We have never been aware of anything like this before," Denise Fennessy, assistant director of Orange County's environmental health division, told the Associated Press.

KABC News explains that Lyn Hiner, 43, had picked up the rocks during a trip to the beach with her family last Saturday. The colorful rocks ended up in her pocket, catching fire later that day, apparently from friction, and leaving her with second- and third-degree burns on her hands and legs in the process. Her husband Rob also suffered burns while trying to put out the flames.

The fire was intense enough to set off smoke alarms, ABC News reports. Orange County Fire Authority Capt. Marc Stone told the network that "there were actual flames coming off of her cargo shorts" when fire officials arrived at the scene. "The husband was outside with a garden hose, actually trying to cool her leg down," he added.

The couple appeared on Good Morning America Friday, where Lyn Hiner explained that he felt something like a "bug bite" on her leg just before her shorts caught fire. She is still recovering at the Grossman Burn Center.

Field tests found phosphorus on two of the seven rocks from Hiner's pocket, with the rest indicating some cross contamination. But it remains unclear how the highly-flammable substance ended up on the rocks in the first place. The AP, however, offers a few possible nearby suspects: Camp Pendleton Marine Base and a local nuclear power plant, which are both near where the rocks were found.