The term depreciation applies only to tangible long-term assets, other than land and natural resources.
Land is not depreciable, because it does not have a limited useful life.
The allocation of the cost of natural resources, such as oil, gas, and timber, to the periods they benefit is referred to as depletion. Natural resources are said to be depleted, not depreciated. Depletion expenses are recorded into accumulated depletion accounts.
Where intangible assets, such as patents, trademarks, or goodwill are involved, the term amortization is employed.

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