It looked like it was made from dirty coal.

This would also give the U.S. some moral high ground in climate change talks with the Chinese as we sell most of our dirty coal to them.

The surrounding strata, if shale or mudstone, often contain slightly more than average and this may also be reflected in the ash content of 'dirty' coals.

Kindan, looking at the dimming light and the dirty coal of the walls, shook his head in disbelief.

That could be important in large developing economies like China's and India's, which would otherwise rely heavily on burning large quantities of dirty coal and oil.

Tell them the dirty coal derived electricity is being turned off.

The new coal can be blended with dirtier coal and burned without smokestack equipment used to control acid rain.

It is also under heavy international pressure to shift from dirtier coal to cleaner energy sources.

We only use nasty dirty coal, for instance, because of the luddite greens.

Their dirty coal power stations provide Beijing with 80% of it's electricity supply, and the pollution in the atmosphere is indescribable.