Property, plant and equipment are depreciated over their useful lives. Useful lives are based on management's estimates of  the period that the assets can generate revenue, which does not necessarily coincide with the remaining term of a customer's  contractual obligation to purchase products made using those assets. The Company's sales of PCC are predominantly  pursuant to long-term evergreen contracts, initially ten years in length, with paper mills at which the Company operates  satellite PCC plants. The terms of many of these agreements have been extended, often in connection with an expansion of  the satellite PCC plant. Failure of a PCC customer to renew an agreement or continue to purchase PCC from a Company  facility could result in an impairment of assets charge or accelerated depreciation at such facility.  Depletion of mineral reserves is determined on a unit-of-extraction basis for financial reporting purposes, based upon  proven and probable reserves, and on a percentage depletion basis for tax purposes.  F-8  The Company records derivative financial instruments which are used to hedge certain foreign exchange risk at fair value  on the balance sheet. See Note 9 for a full description of the Company's hedging activities and related accounting policies.  The recorded amounts of cash and cash equivalents, receivables, short-term borrowings, accounts payable, accrued  interest, and variable-rate long-term debt approximate fair value because of the short maturity of those instruments or the  variable nature of underlying interest rates. Short-term investments are recorded at cost, which approximates fair market  value.  The Company provides for obligations associated with the retirement of long-lived assets and the associated asset  retirement costs. The fair value of a liability for an asset retirement obligation is recognized in the period in which it is  incurred if a reasonable estimate of fair value can be made. The associated asset retirement costs are capitalized as part of the  carrying amount of the long-lived asset. The Company also provides for legal obligations to perform asset retirement  activities where timing or methods of settlement are conditional on future events.  The Company performs a qualitative assessment for each of its reporting units to determine if the two step process for  impairment testing was required. If the Company determines that it was more likely than not that the fair value of a reporting  unit was less than its carrying amount, the Company would then have evaluated the recoverability of goodwill using a two- step impairment test approach at the reporting unit level. In the first step, the fair value for the reporting unit is compared to  its book value including goodwill. In the case that the fair value of the reporting unit is less than book value, a second step is  performed which compares the fair value of the reporting unit's goodwill to the book value of the goodwill. The fair value for  the goodwill is determined based on the difference between the fair values of the reporting unit and the net fair values of the  identifiable assets and liabilities of such reporting unit. If the fair value of the goodwill is less than the book value, the  difference is recognized as an impairment.  Goodwill represents the excess of purchase price and related costs over the value assigned to the net tangible and  identifiable intangible assets of businesses acquired. Goodwill is not amortized, but instead assessed for impairment. Intangible assets with estimable useful lives are amortized over their respective estimated lives to the estimated residual  values, and reviewed for impairment.  Long-lived assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying  amount of an asset may not be recoverable. If events or changes in circumstances indicate that the carrying amount of an  asset may not be recoverable, the Company estimates the undiscounted future cash flows (excluding interest), resulting from  the use of the asset and its ultimate disposition. If the sum of the undiscounted cash flows (excluding interest) is less than the  carrying value, the Company recognizes an impairment loss, measured as the amount by which the carrying value exceeds  the fair value of the asset, determined principally using discounted cash flows.  Stripping costs are those costs incurred for the removal of waste materials for the purpose of accessing ore body that will  be produced commercially. Stripping costs incurred during the production phase of a mine are variable costs that are  included in the costs of inventory produced during the period that the stripping costs are incurred.  Stripping Costs Incurred During Production  Accounting for the Impairment of Long-Lived Assets Goodwill and Other Intangible Assets Accounting for Asset Retirement Obligations Fair Value of Financial Instruments Derivative Financial Instruments MINERALS TECHNOLOGIES INC. AND SUBSIDIARY COMPANIES  NOTES TO CONSOLIDATED FINANCIAL STATEMENTS 