In 2015 , the US produced 12 percent of the world 's phosphate rock .
The United States was the world 's largest producer of phosphate rock from at least 1900 , up until 2006 , when US production was exceeded by that of China .
In 2015 , the US produced 12 percent of the world 's phosphate rock .
The United States was the world 's largest producer of phosphate rock from at least 1900 , up until 2006 , when US production was exceeded by that of China .