leaching. Phosphate leached from guano phosphatizes the underlying rocks in some areas, forming apatite where the host rock is limestone and forming aluminum- or aluminum-iron-phosphate minerals where the underlying rock is a silicate. Individual deposits of both igneous apatite and marine phosÂ­
Medicare Part B (Medical Insurance) covers diagnostic hearing and balance exams if your doctor or other health care provider orders these tests to see if you need medical treatment. Medicare doesn't cover routine hearing exams, hearing aids, or exams for fitting hearing aids.
1 Medicare Part A is hospital insurance. You usually don't pay a monthly premium for Part A if you or your spouse paid Medicare taxes while working. 2  Medicare Part B is medical insurance. You pay a premium each month.  Medicare Part D is pharmacy coverage. You pay a premium each month.