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).
Coke is carbonized coal, a product produced by baking coal in a heated oven. By using a process that allows the impurities in the coal to be burned off, while not allowing the carbon content of the coal to burn, the coal is turned into coke. The impurities burned off were actually the volatile matter contained in the coal, such as tars, oils and gases. When burned, coke generated an intense amount of heat but produced very little smoke, qualities that made it an ideal fuel for use in producing iron and steal. During the 1880's, coke began to replace charcoal in the making of steel at foundries in the United States.