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 latest available estimates of logistics costs from CASS are those for the year 2002. Table 2, based on data from the 14th edition of the CASS Annual State of Logistic Reports, shows that the total logistics costs were $910 billion in 2002, equivalent to 8.7% of the U.S. gross domestic product in the same year.