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Scientists Don't Know Why Rocks Spontaneously Combusted in Woman's Cargo Shorts

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Scientists still aren't completely sure why the rocks a San Clemente woman picked up off the beach spontaneously ignited in her cargo shorts last weekend.

Lyn Hiner, 43, and her children picked up stones streaked with orange from San Onofre State Beach. They burst into flames not long after she got home from the beach, according to the Orange County Register. Once her husband managed to take her flaming shorts off and the rocks fell out, they continued to spark. Hiner was hospitalized by the freakish incident and has undergone two skin graft surgeries to replace burned skin on her thighs.

Scientists say that they've never heard of anything like it and can't easily explain it. So far the best clues were the streaks of phosphorus discovered on the rocks. But how the chemical got there—and why they didn't burst into flames sooner—is a mystery.

Andrew Borovik, a chemistry professor at UC Irvine, said that phosphorus is typically stored in water and could ignite when air touches it. So it's possible that the phosphorus didn't have a reaction with the air until the rocks had dried out. But explaining how the phosphorus got there is still a mystery. James Earthman, a UCI professor of chemical engineering and material science, suggested that the phosphorus could have come a passing ship or Camp Pendleton. (Scientists say it probably has nothing to do with the nearby nuclear plant.)

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Orange County Public Heath is conducting more tests on the rocks, and it could be a few weeks until its results come back.

As freakish as the incident is Hiner said it could have been worse: "I'm grateful it wasn't the girls and that it didn't happen on the freeway on our drive home."

The OC Register has pictures of the rocks, her shorts and the burn marks left behind.