In 2012, the US exported 125,745,662 tons of coal.
http://www.eia.gov/coal/production/quarterly/pdf/t7p01p1.pdf
Our total 2012 exports equaled $1,546,455,000,000.
http://www.census.gov/foreign-trade/Press-Release/2012pr/aip/related_party/rp12.pdf
Coal prices widely vary perhaps $75~150 per ton depending on quality, location, etc. Even at $150/ton, it would be about 1% of our exports.
Thanks for the links. I stand corrected.