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).
Combustion which is a type of redox reaction has been a significant part of human life. Combustion of coal oxidizes the carbon into carbon-dioxide. Rusting of iron is a slow process resulting in a brittle brown substance called rust. Oxidation of copper results is a greenish coating called copper oxide. The combustion that takes place at a rapid rate results in an explosion.