Non-physical assets are expensed to the income statement or profit and loss statement via a method called amortization. It is most commonly used in the mortgage industry to refer to the monthly payment made to pay interest and the principal (the amortizable portion) on a debt instrument.
Depletion is a capital purchase allocation system similar to depreciation and amortization. Depletion is used in mining, oil, and natural resource operations. Depletion is calculated as the amount removed versus the estimated volume on hand.