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).
TYPES OF COAL Coal is classified into four main types, or ranks (lignite, subbituminous, bituminous,anthracite), depending on the amounts and types of carbon it contains and on the amountof heat energy it can produce.ignite is the lowest rank of coal with the lowest energy content. Lignite coal depositstend to be relatively young coal deposits that were not subjected to extreme heat orpressure. Lignite is crumbly and has high moisture content.