A mine is used up. A patent runs out. Neither wears out the way a machine does.
| Depletion expense | 40,000 | ||
| Accumulated depletion—Mine | 40,000 |
| Amortization expense—Patents | 3,000 | ||
| Accumulated amortization—Patents | 3,000 |
are physically removed and sold; allocates their cost per unit extracted, the same logic as units-of-production depreciation.
— a , , or — have no physical form but a real legal life. spreads their cost over that life. is the one exception: never amortized, only tested for when its value might have fallen.