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.
While there are cost efficient vacations available â you can even staycation at home â it will cost you to pick up and go this summer. According to American Express, the average vacation expense per person in the United States is $1,145, or $4,580 for a family of four. When youâre calculating the cost of your vacation, donât be fooled by the proposed cost on hotel rooms and airfare. What is often missing from those figures as you book can be significant: taxes. Travel-related taxes can boost your travel cost by more than 50%.