While most experts agree that only a small percentage of granite in homes today poses any health risk, the current debate centers on identifying granite that might emit radiation and determining under what circumstances a danger occurs.

"The vast majority of granites in the vast majority of houses are not going to be a problem," said Daniel Steck, a physics professor at St. John's University in Collegeville, Minn., and head of the Minnesota Radon Project. Steck has tested about 250 granites. Of those, none emitted enough radiation to be a concern, he said.

But a small minority, about 5%, appeared to contribute enough radon to pose "a mild problem" when used in large quantities or in a small, tightly sealed home.

You can't spot a hot slab by its looks, color or its name. Granite names are variable, and stones with the same name can have different geological content, Steck said. Right now, "There's no good way to identify that 5%."

As demand for granite has increased, exotic stones are being imported from remote corners of the world and greater scrutiny is needed, said William Llope, a nuclear physicist at Rice University in Houston. Llope started testing granites as a hobby after he was asked to test a countertop and was surprised at the level of radiation.

"It's an uncontrolled situation," he said. "The majority of granites are quiet," with radiation levels that are negligible when compared to background radiation. But there are now about 2,000 granites being exported from about 70 countries, he noted. Some quarries within miles of uranium mines.

"Some stones from Namibia and Brazil are wicked hot." Still, the health risk is ambiguous and probably long-term.

"You're not going to spend six months in your kitchen and die of cancer," Llope said. But extended exposure to the hottest granites he's tested has the potential to increase lifetime cancer risk, especially for young children.

Many in the industry believe that any risk is being wildly overblown by those with commercial motives. Guido Gliori, president of the Marble Institute, says that some of the research linking granite and radiation has been funded by manufacturers of competing countertop materials, including Cambria, the company that produces quartz countertops.