Mr. Obama rarely plays with other politicians - though he has played 7 times with Vice President Biden. In a fence-mending gesture, Mr. Obama invited then-House Speaker John Boehner to play on one occasion in June 2011 along with Gov. John Kasich, both Ohio Republicans.
Here are some ways to classify coal (by grouping it with similar types of rocks): Because slag formed from lava-like melted rock, it's sort of like an igneous rock -- but because humans made the melt, it's not a true igneous rock. So, we made up a new classification for slag: We call it a pseudo-igneous rock (pronounced SUE-doe ig-NEE-us).
A curmudgeon with years of practice. Coal ash is the residue from burning coal and contains all of the nonvolatile components of he coal (carbon compounds, sulfur and some metals). The ash is made up of silicates, metals (including toxic metals like mercury and uranium) and some unburnt carbon.