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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-Q

x QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE

SECURITIES EXCHANGE ACT OF 1934

For the quarterly period ended June 30, 2012

OR

¨ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE

SECURITIES EXCHANGE ACT OF 1934

For the transition period from              to             .

Commission File Number: 1-8944

CLIFFS NATURAL RESOURCES INC.

(Exact Name of Registrant as Specified in Its Charter)

Registrant’s Telephone Number, Including Area Code: (216) 694-5700

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.

YES  x                                         NO  ¨

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).

YES  x                                         NO  ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act.

Large accelerated filer  x             Accelerated filer  ¨    Non-accelerated filer   ¨    Smaller reporting company  ¨

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).

YES  ¨                                         NO  x

The number of shares outstanding of the registrant’s Common Shares, par value $0.125 per share, was 142,492,567 as of July 23, 2012.

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Definitions

The following abbreviations or acronyms are used in the text. References in this report to the “Company,” “we,” “us,” “our” and “Cliffs” are to Cliffs Natural Resources Inc. and subsidiaries, collectively. References to “A$” or “AUD” refer to Australian currency, “C$” to Canadian currency and “$” to United States currency.

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PART I - FINANCIAL INFORMATION

ITEM 1 - FINANCIAL STATEMENTS

CLIFFS NATURAL RESOURCES INC. AND SUBSIDIARIES

STATEMENTS OF UNAUDITED CONDENSED CONSOLIDATED OPERATIONS

The accompanying notes are an integral part of these unaudited condensed consolidated financial statements.

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CLIFFS NATURAL RESOURCES INC. AND SUBSIDIARIES

STATEMENTS OF UNAUDITED CONDENSED CONSOLIDATED COMPREHENSIVE INCOME

The accompanying notes are an integral part of these unaudited condensed consolidated financial statements.

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CLIFFS NATURAL RESOURCES INC. AND SUBSIDIARIES

STATEMENTS OF UNAUDITED CONDENSED CONSOLIDATED FINANCIAL POSITION

The accompanying notes are an integral part of these unaudited condensed consolidated financial statements.

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CLIFFS NATURAL RESOURCES INC. AND SUBSIDIARIES

STATEMENTS OF UNAUDITED CONDENSED CONSOLIDATED CASH FLOWS

The accompanying notes are an integral part of these unaudited condensed consolidated financial statements.

See Note 20 - Cash Flow Information.

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CLIFFS NATURAL RESOURCES INC. AND SUBSIDIARIES

NOTES TO UNAUDITED CONDENSED CONSOLIDATED FINANCIAL STATEMENTS

June 30, 2012

NOTE 1 – BASIS OF PRESENTATION AND SIGNIFICANT ACCOUNTING POLICIES

The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with SEC rules and regulations and in the opinion of management, contain all adjustments (consisting of normal recurring adjustments) necessary to present fairly, the financial position, results of operations, comprehensive income and cash flows for the periods presented. The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Management bases its estimates on various assumptions and historical experience, which are believed to be reasonable; however, due to the inherent nature of estimates, actual results may differ significantly due to changed conditions or assumptions. The results of operations for the three and six months ended June 30, 2012 are not necessarily indicative of results to be expected for the year ended December 31, 2012 or any other future period. These unaudited condensed consolidated financial statements should be read in conjunction with the financial statements and notes included in our Annual Report on Form 10-K for the year ended December 31, 2011.

The unaudited condensed consolidated financial statements include our accounts and the accounts of our wholly owned and majority-owned subsidiaries, including the following operations:

Intercompany transactions and balances are eliminated upon consolidation.

Also included in our consolidated results are Cliffs Chromite Ontario Inc. and Cliffs Chromite Far North Inc., which have a 100 percent interest in the Black Label and Black Thor chromite deposits and a 72 percent interest in the Big Daddy chromite deposit, all located in Northern Ontario, Canada.

The following table presents the detail of our investments in unconsolidated ventures and where those investments are classified in the Statements of Unaudited Condensed Consolidated Financial Position as of June 30, 2012 and December 31, 2011. Parentheses indicate a net liability.

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Immaterial Errors

In September 2011, we noted an error in the accounting for the 21 percent noncontrolling interest in the Empire mine. In accordance with applicable GAAP, management quantitatively and qualitatively evaluated the materiality of the error and determined the error to be immaterial to the quarterly reports previously filed for the periods ended March 31, 2011 and June 30, 2011 and also immaterial for the quarterly report for the period ended September 30, 2011. Accordingly, all of the resulting adjustments were recorded prospectively in the Statements of Unaudited Condensed Consolidated Operations for the three and nine months ended September 30, 2011 and the Statements of Unaudited Condensed Consolidated Financial Position as of September 30, 2011. The impact of the immaterial error in the Statements of Unaudited Condensed Consolidated Operations for the three and six months ended June 30, 2011 would have resulted in an increase in Income from Continuing Operations of $7.7 million and $16.1 million, respectively, and a decrease in Net Income Attributable to Cliffs Shareholders of $30.4 million and $67.9 million, respectively, or $0.22 and $0.49, respectively, to basic and diluted earnings per common share. These adjustments should be considered when comparing the operating results for the three and six months ended June 30, 2012 to the reported results for the three and six months ended June 30, 2011, as such adjustments are not reflected in the operating results reported for the three and six months ended June 30, 2011.

Discontinued Operations

On September 27, 2011, we announced our plans to cease and dispose of the operations at the renewaFUEL biomass production facility in Michigan. As we continued to successfully grow our core iron ore mining business, the decision to sell our interest in the renewaFUEL operations was made to allow our management focus and allocation of capital resources to be deployed. On January 4, 2012, we entered into an agreement to sell the renewaFUEL assets to RNFL Acquisition, LLC. The results of operations of the renewaFUEL operations are reflected as discontinued operations in the accompanying unaudited condensed consolidated financial statements for all periods presented. We recorded a loss of $0.1 million as Loss From Discontinued Operations in the Statements of Unaudited Condensed Consolidated Operations for the six months ended June 30, 2012. This compares to losses of $0.7 million and $1.1 million for the three and six months ended June 30, 2011.

Significant Accounting Policies

A detailed description of our significant accounting policies can be found in the audited financial statements for the fiscal year ended December 31, 2011, included in our Annual Report on Form 10-K filed with the SEC. There have been changes in our significant accounting policies from those disclosed therein. As disclosed in the March 31, 2012 Form 10-Q, the following significant accounting policies have been included within the disclosures below.

Revenue Recognition and Cost of Goods Sold and Operating Expenses

U.S. Iron Ore, Eastern Canadian Iron Ore and Asia Pacific Iron Ore

We sell our products pursuant to comprehensive supply agreements negotiated and executed with our customers. Revenue is recognized from a sale when persuasive evidence of an arrangement exists, the price is fixed or determinable, the product is delivered in accordance with F.O.B. terms, title and risk of loss have transferred to the customer in accordance with the specified provisions of each supply agreement and collection of the sales price reasonably is assured. Our U.S. Iron Ore, Eastern Canadian Iron Ore and Asia Pacific Iron Ore supply agreements provide that title and risk of loss transfer to the customer either upon loading of the vessel, shipment or, as is the case with some of our U.S. Iron Ore supply agreements, when payment is received. Under certain term supply agreements, we ship the product to ports on the lower Great Lakes or to the customers’ facilities prior to the transfer of title. Our rationale for shipping iron ore products to certain customers and retaining title until payment is received for these products is to minimize credit risk exposure.

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Iron ore sales are recorded at a sales price specified in the relevant supply agreements resulting in revenue and a receivable at the time of sale. Upon revenue recognition for provisionally priced sales, a freestanding derivative is created for the difference between the sales price used and expected future settlement price. The derivative, which does not qualify for hedge accounting, is adjusted to fair value through Product revenues as a revenue adjustment each reporting period based upon current market data and forward-looking estimates determined by management until the final sales price is determined. The principal risks associated with recognition of sales on a provisional basis include iron ore price fluctuations between the date initially recorded and the date of final settlement. For revenue recognition, we estimate the future settlement rate; however, if significant changes in iron ore prices occur between the provisional pricing date and the final settlement date, we could be required to either return a portion of the sales proceeds received or bill for the additional sales proceeds due based on the provisional sales price. Refer to NOTE 3 – DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES for further information.

In addition, certain supply agreements with one customer include provisions for supplemental revenue or refunds based on the customer’s annual steel pricing for the year the product is consumed in the customer’s blast furnaces. We account for this provision as a derivative instrument at the time of sale and record this provision at fair value until the year the product is consumed and the amounts are settled as an adjustment to revenue. Refer to NOTE 3 – DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES for further information.

Revenue from product sales also includes reimbursement for freight charges paid on behalf of customers in Freight and venture partners’ cost reimbursements separate from Product revenues. Revenue is recognized for the expected reimbursement of services when the services are performed.

Costs of goods sold and operating expenses represents all direct and indirect costs and expenses applicable to the sales and revenues of our mining operations. Operating expenses within this line item primarily represent the portion of the Tilden mining venture costs for which we do not own; that is, the costs attributable to the share of the mine’s production owned by the other joint venture partner in the Tilden mine. The mining venture functions as a captive cost company; it supplies product only to its owners effectively on a cost basis. Accordingly, the noncontrolling interests’ revenue amounts are stated at cost of production and are offset by an equal amount included in Cost of goods sold and operating expenses resulting in no sales margin reflected in the noncontrolling partner participant. As we are responsible for product fulfillment, we act as a principal in the transaction and, accordingly, record revenue under these arrangements on a gross basis.

Where we have joint ownership of a mine, our contracts entitle us to receive royalties and/or management fees, which we earn as the pellets are produced.

Recent Accounting Pronouncements

In May 2011, the FASB amended the guidance on fair value as a result of the joint efforts by the FASB and the IASB to develop a single, converged fair value framework. The amended fair value framework provides guidance on how to measure fair value and on what disclosures to provide about fair value measurements. The significant amendments to the fair value measurement guidance and the new disclosure requirements include: (1) the highest and best use and valuation premise for nonfinancial assets; (2) the application to financial assets and financial liabilities with offsetting positions in market risks or counterparty credit risks; (3) premiums or discounts in fair value measurement; (4) fair value of an instrument classified in a reporting entity’s shareholders’

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equity; (5) for Level 3 measurements, a quantitative disclosure of the unobservable inputs and assumptions used in the measurement, a description of the valuation process in place, and a narrative description of the sensitivity of the fair value to changes in the unobservable inputs and interrelationships between those inputs; and (6) the level in the fair value hierarchy of items that are not measured at fair value in the Statement of Financial Position but whose fair value must be disclosed. The new guidance is effective for interim and annual periods beginning after December 15, 2011. We adopted the amended guidance as of January 1, 2012. Refer to NOTE 8 – FAIR VALUE OF FINANCIAL INSTRUMENTS for further information.

NOTE 2 – SEGMENT REPORTING

Our Company’s primary operations are organized and managed according to product category and geographic location: U.S. Iron Ore, Eastern Canadian Iron Ore, North American Coal, Asia Pacific Iron Ore, Asia Pacific Coal, Latin American Iron Ore, Ferroalloys and our Global Exploration Group. The U.S. Iron Ore segment is comprised of our interests in five U.S. mines that provide iron ore to the integrated steel industry. The Eastern Canadian Iron Ore segment is comprised of two Eastern Canadian mines that primarily provide iron ore to the seaborne market for Asian steel producers. The North American Coal segment is comprised of our five metallurgical coal mines and one thermal coal mine that provide metallurgical coal primarily to the integrated steel industry and thermal coal primarily to the energy industry. The Asia Pacific Iron Ore segment is located in Western Australia and provides iron ore to the seaborne market for Asian steel producers. There are no intersegment revenues.

The Asia Pacific Coal operating segment is comprised of our 45 percent economic interest in Sonoma, located in Queensland, Australia. The Latin American Iron Ore operating segment is comprised of our 30 percent Amapá interest in Brazil. The Ferroalloys operating segment is comprised of our interests in chromite deposits held in Northern Ontario, Canada and the Global Exploration Group is focused on early involvement in exploration activities to identify new projects for future development or projects that add significant value to existing operations. The Asia Pacific Coal, Latin American Iron Ore, Ferroalloys and Global Exploration Group operating segments do not meet reportable segment disclosure requirements and therefore are not reported separately.

We evaluate segment performance based on sales margin, defined as revenues less cost of goods sold and operating expenses identifiable to each segment. This measure of operating performance is an effective measurement as we focus on reducing production costs throughout the Company.

The following table presents a summary of our reportable segments for the three and six months ended June 30, 2012 and 2011:

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