Parts of the teeth include: 1  Enamel: The hardest, white outer part of the tooth. Enamel is mostly made of calcium phosphate, a rock-hard mineral. 2  Dentine: A layer underlying the enamel. Dentine is made of living cells, which secrete a hard mineral substance.  Pulp: The softer, living inner structure of teeth.
Though they vary significantly, transportation costs accounted for 40% of the average overall cost of coal delivered at electric power plants in 2010. On average, nominal U.S. rail rates for shipping coal grew from $11.83 to $17.25 per short ton from 2001 to 2010.
The cost of operating the U.S. business logistics system in 2014 rose 3.1 percent to slightly less than $1.45 trillion, equal to about 8.3 percent of the nation's gross domestic product (GDP), according to the 26th annual State of Logistics Report, released on Tuesday in Washington, D.C.