"The lower gas prices are hurting the whole sector," said Jeremy Sussman, an analyst with Brean Murray Carret & Co.

Natural gas July futures on the New York Mercantile Exchange NGN0 slid 9.3 cents, or 2.14 percent, to settle at $4.248 per million British thermal units.

That caused concern for investors, the analysts said, since lower prices make gas an attractive alternative to coal for power-generating utilities.

Also driving the coal sector down was the euro falling to a four-year low against the dollar, which can lower revenues, they said.

Sussman noted that miners specializing in steel-making metallurgical coal -- Alpha Natural Resources and Walter Energy -- were hit harder because of concerns over a slowing Chinese economy from factory output data released earlier on Tuesday.

At the close of trading on the New York Stock Exchange, Alpha fell 10.7 percent to $34.26 and Walter fell 11.17 percent to $70.47.