Yet another cancer cause to add to the list.

The sounds of children playing baseball has been silenced at one ball field in this western North Dakota city. Officials fear the ground itself is simply too unsafe.

The ballpark, one of two in this town of about 700 people, is covered with crushed gravel containing erionite, a mineral found in the chalky white rock mined from the nearby Killdeer Mountains.

The rock, used for decades on everything from gravel roads to flower beds, contains fibers that can collect in the lungs of people who breathe it, health officials say.

Steve Way, a federal Environmental Protection Agency coordinator, said studies have shown that erionite causes cancer in lab rats, though the mineral is not regulated by his agency.